My Background
I have played just about every edition of D&D after the white box, and I play 4E. I'm currently running a 4E campaign that intentionally breaks the Gamist expectations of the rules. I occasionally play in a "Western Marches"-style Darksun 4E campaign that very much adheres to the Gamist expectations of the rules.
Gamism as I define it is a type of play in which the group of players are all interested in being tested by tough challenges and showing what they're made of (as players, not characters). It doesn't preclude creating story or developing a character (personality) or making tough moral decisions or immersing in a fantasy world, but these things take a back seat to the primary goal of play: winning challenges.
Can you play D&D 4E in a non-Gamist way? Yes, obviously. You have to break the reward cycle to do it, though, and the 4E reward cycle is very strong. Breaking the reward cycle means ignoring some of the rules, and if you ignore too many rules, are you still playing 4E?
The Reward Cycle
When I talk about the reward cycle of 4E, I mean the internal currency mechanism that rewards players for a certain kind of play. The basic cycle is this:
Players make some tough choices about their characters. The first thing they do is create a character, but this also includes choices made during play, and choices made between levels.
Players pit their characters against all manner of dangerous challenges. This rewards them (the players) with feedback about how good their choices are.
Players reward each other with feedback about how good they think everyone else's choices were. "Great job, Adam! Your fighter totally saved the lives of everyone in the party because you blocked that narrow door!"
Players earn experience points (XP) and treasure. These are types of game currency that make their characters stronger. Stronger characters can face tougher challenges! This changes play dramatically. This changes the types of decisions players will make during play.
The end of that cycle feeds back into the beginning again. Players take the feedback from the game play, feedback from the group, and the in-game currency, and apply that to new choices. The new choices include new character options when leveling up, and new tactics and strategies "in the dungeon" (or wherever).
Note that my examples are all combat and treasure, but this applies for other parts of the 4E game, like skill challenges.
Also note that I leave the roleplaying stuff out. While this is an important part of play for most people and the rules do talk about roleplay, the rules don't specifically include roleplay in the reward cycle. You earn XP by defeating monsters, by overcoming challenges, and by completing quests. Any house rule that awards XP for good roleplay must award enough XP to overshadow the normal XP awards to have any real impact, too.
Breaking the Reward Cycle
It's hard!
In my Saberpunk campaign, I basically just keep mental track of how many meaningful "scenes" the party finishes and award a new level to the group every ten scenes. Scenes include any kind of interesting conflict that the party faces. Combats are obviously part of that, as well as skill challenges, but some of these scenes are resolved with simple choices and roleplay. I give out treasure at a much slower rate than the book suggests.
So I cut the cord at the currency end of things. However, the leveling is still there. That means the power level still changes and the players are rewarded with shiny new powers and new challenges to face. Those things are a strong pull for players, who inevitably want to see their characters' new powers in action.
My Saberpunk campaign is, as I expected, drifting back to Gamist play. I'd intended a more Sim game built around a cyberpunk mood and setting. That stuff is still there, but it's getting lost. Our sessions are moving back to the "one or two big combats" that I was trying to avoid. The players have actively voiced wanting those combats and I won't deny them the fun they want.
At the same time, 4E doesn't entirely do what I need it to do. The Sim style of play I want begs for some additional character skills (in this case, Perform for the bard, and an Espionage skill for the wizard -- though Insight will do in a pinch). We just hack those in with a house rule. I'm using the Obsidian Skill Challenge system, too, with great success. I use a Blood Points rule to reducing whiffing and make combats less deadly.
This is just my latest attempt in a handful of failed attempts to drift D&D away from Gamist play. Even older versions have a reward cycle much the same as 4E's. My 3.5E campaigns trended the same way, even with significant XP awards for playing to specific, player-written goals/beliefs. While the XP awards were significant enough to make killing stuff less important, the reward of leveling and getting new character abilities was more powerful, drawing players into combats just to see their higher-level character do his or her thing.
The game gives you an asskicking character, and players want to kick some ass.
What is 4E anyway?
How far can you bend (or ignore) the rules of a game until it's no longer that game? There's no one answer to this question, for sure, but my personal feeling is that you should be able to bring in an average 4E player off the street and, without telling him what you're playing, he should recognize the game.
4E is, at its core, about 50 pages of actual "framework" rules. Most of the rest is rules-by-exception stuff: character race and class lists, magic item lists, equipment lists, skill lists, ritual lists, and monster lists. Some of the rest is play advice. The core of the 50 framework pages is the reward cycle. That includes: rules for creating a character (minus race and class definitions), fighting monsters, handling skill challenges, awarding XP, and leveling up.
When you start ignoring the core stuff, you start drifting away from 4E. I replaced the leveling up system with my own system (which happens to be very similar to a variant in the DMG2, though). I replaced the skill challenge system with Obsidian. I tweaked some rules to make combats more fun (like Blood Points, and like letting characters make a skill check as a Move Action instead of a Standard Action).
However, if Joe 4E Player came into my house on alternating Thursday nights, he'd recognize what we were doing as 4E. It might annoy the crap out of him though, since I totally de-emphasize the getting-into-combat stuff, which is the bread and butter of a lot of 4E games.
When I hear people say that they run games where there are never combats and no one rolls any dice, I wonder why they still insist on calling that D&D, let alone D&D 4E. What about it is 4E? I could bring a GURPS Fantasy character, or a D&D 1st Edition character, or a Rifts character into that game and play, right?
If "playing 4E" means using all the rules as written, I'd say that it's nearly impossible to stop playing it in a Gamist way and still have fun. You'd have to build characters, fight monsters, overcome skill challenges, earn XP, level up, and not care about that reward cycle. Let's say you're interested more in reinforcing the cyberpunk-infused-D&D tropes of the Saberpunk world than kicking ass. You're still fighting monsters. You're still earning XP. You level up a few times, and now your character definition includes a bunch of new powers. To use them, you need to level up more. You don't want to die, either, so you start applying the best tactics you have. Maybe you choose powers that make better sense as a build option than a character-development option. You're headed back to Gamism.
But very few people play using all the rules. Say you're like most games and you have a handful of house rules and you ignore some other rules, like I do with Saberpunk. It's still easily recognized by the average 4E player as "4E" and not some other D&D edition or some other RPG. The rules-as-written even tell DMs it's okay to tweak things. So is playing "4E" the same as playing 4E? I don't know. If you have to modify or ignore the rules to get some kind of non-Gamist play out of the system, is it really fair to say you're playing 4E? It's a philosophical point, and I grant that it doesn't have an easy answer.
Can you house-rule 4E so that it supports non-Gamist play and is still recognizable to 4E players? Sure. I recommend starting everyone at a higher level, tossing out XP and leveling altogether, deemphasizing the combats, and focusing on the kind of play you want. But now that you've thrown out the core of what makes 4E a D&D game, why didn't you just use a different ruleset to begin with?
Yes, there is a good reason for feat prerequisites.
Two reasons, in fact:
To clarify by indicating what build a feat is intended for (a feat that boosts Lay on Hands usually requires that you have Lay on Hands)
To balance by forcing players to dedicate more resources in order to take a more powerful feat.
I suspect the reason you're surprised to encounter this is that by and large 4e feat prerequisites are for clarity: if there's a feat we want, we probably already qualify for it. (In previous editions of D&D prerequisites were much harsher and it was common to plan our characters around qualifying for certain feats.) It's surprising to find a feat we want that we can't take in 4e.
Mastery feats need to be balanced carefully:
Feats like the Mastery set can be very powerful: they double crit range from 1/20 to 1/10, and for a build that 'fishes' for critical hits that's pretty massive (other builds wouldn't be as impressed by it, but a feat's value shouldn't be based on its usefulness to a character that wouldn't take it anyway). Consider a burst/blast wizard who attacks an average of 4 targets each round: compared to a character with expanded crit who makes one attack in the same time, the wizard with expanded crit will deal maximum damage every 3 rounds instead of every 10. If he has specialized in making his criticals awesome, this is very powerful.
In order to allow such feats to exist without unbalancing the system 4e has imposed more stringent prerequisites to take them. But...
The requirements really aren't that harsh:
Prerequisite: 21st level, Dex 15, Int 21, Wis 15, wizard
At level 21 two of a character's abilities can have increased by +6, and the other four abilities have increased by +2. This means that for Wizard Implement Expertise I can start with (before racial modifiers, assuming I take a race with +Int) a 13 Int, Dex, and Wis to qualify at 21 without focusing on either of those secondary stats or having racial bonuses to them. Roughly two out of every three wizards will have focused on at least one of them, and it's important to remember that the 4e stat generating system makes it impossible for me to start with less than a 14 in at least one stat.
A player who wants the feat should have been considering it ahead of time and planned accordingly--but even a wizard who hadn't planned to get the feat is likely to qualify. (If I want it so bad anyway, I've got two +1 stat bumps at 24 and 28 to bring my 11 up to a 13 and still enjoy the feat for the last three levels of the game.)
Sure, change it if you like.
The phrase "feat tax" gets thrown around a lot. It seems to mean that there are specific feats I need to take in order to not be a burden on my party. I generally disagree with this idea because it presupposes a specific kind of character optimization which is just one style of play rather than a philosophy of the game design.
Feat slots are limited for a reason: to force choice. There are better and worse choices, though 4e has done a surprisingly good job of limiting downright awful choices. By lifting feat prereqs and granting free feats, your group would be saying these choices aren't part of the kind of game they want to play.
And if that's your party's play style, go for it: there's no wrong way to play the game provided everyone's safe and happy. But it's not the way the game was designed, and the game wasn't designed by accident (however much I joke about the adventure writers), so we're less surprised by mechanics like these if we understand the original philosophy behind them.
Best Answer
It's definitely common. I'm in one campaign that uses it, and you see it suggested an awful lot.
Many people feel expertise bonuses are necessary to make the math work. Here's the deal: if you extrapolate a character's attack bonuses and a monster's defenses, incorporating expected magic items and so on, the attack bonuses increase slower than the defenses. Therefore, without looking at any other factors, the characters hit less often as they level.
At level 1, a typical melee character has +4 to hit from his stats, +0 from his level, and let's say a +3 proficiency bonus from his weapon. That's a +7 to hit, versus a typical AC of 15 for a level 1 monster.
At level 30, the same character has +8 to hit from his stats, +15 from his level, +3 proficiency bonus from his weapon, and the weapon is +6 as well. That's a +32 to hit, but the monster has an AC of 44.
However, the PCs also get more situational bonuses as they go up in level. With higher level powers, they're more able to tilt the scales back in their direction; they have more ways to get combat advantage, more ways to reduce a monster's defenses, and so on. Some people feel these advantages even out the playing field such that the advantages you get from the Expertise feats are not necessary.
I can say that at paragon tier, I've found my PCs to be more effective against monsters due to those factors, but that is just one person and I can't at all speak to epic tier. There are some interesting threads here and here.
However, no matter which side of the fence you fall on, I think it's a good idea to do one of two things: either give everyone the expertise feats for free (you want to give out Implement Expertise as well, I note) or remove them entirely. The thing is, they're good enough so that people will usually wind up taking them at some point. If you think you need them, you'll take them immediately; if you don't think you need them, they're still worth taking if you want to make your character even more accurate.
Finally, it's worth noting my two sneaky little secrets about 4e. First, optimization doesn't matter. The game plays just fine if you have a 16 in your primary stat. I play a halfling barbarian, I spent the points to get an 18 Strength, and if you listen to the optimizers I'd have made a mistake and shorted myself elsewhere. But he's a blast.
Second, player skill matters at least as much if not more than optimized characters. If you show me a character with one of the expertise feats who's played by someone who doesn't get the importance of working with his group, and a character without any expertise feats who's played by someone who knows how to stay out of the way of his friend's area spells? I'll play with the latter and we'll have an easier time with the combats.