League-of-legends – When, after acing the enethe team, is it beneficial to go for the inhibitor rather than getting Baron

Sadly, there's no sure-fire way of resolving this situation.

You won't be able to rely on minions to take out their towers and nexus, especially if their uber status gets to the point where they can start defending their respawning inhibitors. If you get really lucky and get their nexus towers down, you could just farm minions hard enough for yours to take the nexus down a bit then try to dive the nexus. I'd consider this a Hail Mary more than anything else, though.

If you know you're going up against a team that is going to steamroll you once they get maxxed out (2+ carries), the main goal is to take advantage of the fact that they will be weaker in the early game. If you zone the carries and/or kill them enough to keep them from getting geared and leveled, your team will get powerful enough to take their nexus before they can do anything about it.

Assuming you find yourself in that unfortunate position anyway and forcing their team to split up isn't working, you absolutely have to focus the primary damage dealers down first. If they stick together and you're not killing their carries first, you'll take way more damage than you will deal out over the course of the fight and you're sure to lose.

It should first be said that the metagame always has the ability to change at any given time. Several factors impact this heavily, namely success found in tournaments by the competitive professional teams.

As seen at IEM Hannover, the meta game between the three regions is essentially the same. All of them utilize AP mid, ranged AD with support bot, jungler, and either a bruiser top or AP, depending on what team comp they were going for and counterpicking. This has effectively been the metagame in all regions, and until someone comes with a different metagame that does well against it in a tournament setting, it will likely stay.

Prior to Dreamhack, the NA meta (can't say US only, since many players from Canada play, for instance of several members of CLG and TSM are Canadian citizens - at WCG: ChaoX, TheOddOne, HotshotGG, BigFatLP, and Elementz represented Canada) ran quite differently to EU. NA teams at the competitive level ran a tank top, jungle, AP mid, ranged and support bot, while EU teams ran double AP in solo lanes, jungle, ranged and support bot. The casual games on NA was still running, double tank lanes bot, AD carry mid, AP top with jungle, and many games had no jungler. I know this because this is when I started playing LoL heavily. At Dreamhack, it showed that EU was more used to AD with support bot, and great plays were made continually by their bot lanes. The eventual winner of course was fNatic led by xPeke and Shuushei showing off their double AP comp to quickly burst the enemy team with AoE damage and making it easy pickings for their AD to finish everything off.

Flash forward to IEM GamesCom, the NA teams now having chance to get more practice with the AD/support bot lanes and think of ways to counter the double AP strategy. NA teams, come up with tanky DPS top and tanky DPS jungle giving way to the Bruiser meta. In one game of TSM against an EU team I cannot remember, TSM takes Soraka/Jax bot lane to combat the Urgot who had given them problems the game before. They had three bruisers and managed to pull off the win before falling to CLG in the finals where the first two games was playing protect the KogMaw.

To answer your question then, it wasn't really a matter of teams playing different metagames, however they understand what counters what and know how to play accordingly. Double AP gets countered by a bruiser/tanky DPS comp. AoE team comps can win teamfights but can be slaughtered to a poke comp where they don't allow a teamfight to happen before they poke you down too much, a push comp counters a poke comp. So counterpicking, and strategies to execute is used a lot to help gain the advantage. For instance, picking a very strong late game comp against an early game team comp and playing super passive to stall the game. Nasus, Irelia, Karthus, Vayne, KogMaw are examples of champions that have an insane lategame but an early game that can be shut down (not so much in the case of pre-nerf Irelia). On the other hand, Urgot, Ezreal, LeBlanc, Alistar, Udyr start to fall off heavily in the late game compared to their counterparts unless they have built up a big item advantage.

As for everyone knowing and following the meta, it can be both a benefit and negative depending on what side you take. In many tournaments, teams have picked like they were following the meta, but in game swap lanes to give themselves the advantage. This is most common with top and bot lanes switching. It also happens with mid lane and top lane as most players use their runes to give themselves a laning advantage. For example, let's say one team's top and mid are Malphite and Galio respectively. The enemy uses Riven and Karthus. Malphite thinking they will face Riven, choose to use a full armor page to effectively negate most of Riven's harass combined with Malphite's passive. Galio similarly use full magic resist page to negate anything Karthus can do in lane. Lane starts and you find they swapped on you. The difference is they could have chosen to rune for it or not, but either way, Malphite and Galio is at a disadvantage since their runes do little for them. Sure Malphite's damage builds with armor and Galio gets more AP with magic resist, but they aren't going to have much fun in the lanes. To compensate, they try to quickly switch. But the enemy team can switch as well, forcing another switch or unfavorable matchup. Each time you switch lanes though, one of your lanes will tend to fall behind, and since you made the first switch, your team will lose out allowing the other team to gain an advantage.