The best way to judge what classes should have access to a spell is to compare it to the kind of spells those classes already have.
Wizard and Sorcerer compulsions tend to be forceful in method and drastic in effect: The examples you gave describe subverting the victim's normal mental process by forcibly inserting a foreign thought, and blatantly stealing control of the victim's mind.
Clerical spells, on the other hand, tend to use more straightforward methods of achieving their ends, and often express the role of clerics as spiritual leaders: Thus, the spells that allow them to speak with authority and be obeyed.
As for why the power of Power X isn't compelling... Well, if you look at the ecology of gods as described in, for example, the Planescape setting, belief is the food of the gods - without it, they lose strength and eventually starve to death, or at least enter a state that is for most practical purposes equivalent to death. A follower who only vaguely follows their patron deity's teachings is still more faithful, and therefore more valuable, than an unbeliever magically compelled to serve. Of course, individual gods might have a thing for magical compulsion, but that's not enough for something to get included in the standard priesthood package.
Oh, and like mxyzplk suggests, there's more game design-y reasons for it, too: if Clerics were good at all forms of magic, they'd be far superior to wizards, even enchanters - and playing an enchanter would be much less interesting.
The reason things are worded so badly lies in the 3.0->3.5->PF transition. See below for that! I believe chill touch is still resolvable using the RAW, though.
Chill Touch
The answer to the chill touch question lies in the rules for holding the charge:
Touch Spells and Holding the Charge: In most cases, if you don't discharge a touch spell on the round you cast it, you can hold the charge (postpone the discharge of the spell) indefinitely. You can make touch attacks round after round until the spell is discharged. If you cast another spell, the touch spell dissipates.
Most touch spells discharge after a single successful attack, but chill touch makes it clear that this isn't the case. Instead, you get one touch per level. So the quoted rule allows chill touch to be used across multiple rounds; there's no need for the spell to explicitly state it. (Though it probably should, just for clarity.)
Willing targets
The rules do explicitly state that you can't hold the charge on multiple targets, so no help there! That seems to be the simplest solution, though.
As an aside, an effect that changes the range of touch spells would "unlock" the full number of targets, so there is a technical difference between the current state and your alternate wording. :P
A little bit of history
So why are the RAW in this state? Well, I did a bit of digging, and this thread was very helpful, especially this post by Hypersmurf. (Who I remember from when I posted in the enworld rules forum far too often -- thanks Hypersmurf!)
In 3.0, you could touch 6 willing targets as a full round action, or one as a standard. There was no restriction on touching all the targets the round the spell finished -- in this context the 6 target limit played well with multi-target spells.
In 3.5, the Magic Overview section was changed: the limit of 6 was removed, but the requirement of touching the targets in a single round was added. However, the rules for touch spells in combat left the old restriction of 6 targets in place. The text here directly contradicted that of the overview section. If you assume that the wording of the overview section was what the designers intended, this would still cause no problems with touch spells targeting multiple willing creatures.
In PF, both limitations are included in the overview. I would assume that someone was trying to reconcile the contradiction mentioned in 2, without realizing that it was a holdover from an intended 3.0->3.5 shift. The result? Accidental nerfing of multi-target touch range buffs.
Likewise, the wording of chill touch has been essentially unchanged since 3.0. It's been edited a little to make the wording less clumsy, but not updated to account for the changing touch attack rules. This explains why it doesn't explicitly call out that it carries across multiple rounds.
Best Answer
It's targeted at 1 creature. It affects 1 creature.
This is not an area attack, it's a directed attack. It's not a spell attack, so the additional creature doesn't grant cover, or even advantage.
Only the target is directed to make a saving throw or take damage so he is the only one affected.
It's worth noting that although this seems less directed than a ranged attack, the rule is similar. Basically everyone is moving all around in their space, you couldn't be shooting your poison at someone in an intervening space, but past them. The way I'd picture this is that those folks might get a whiff of the poison, but it's less of a puff and more of a directed jet at the target.
"Living Rules" is simply a way of talking about how they plan to make system updates and has no effect on a ruling in a case like this. A DM, I suppose, could use the freedom they are granted to make a ruling that additional creatures are affected, but it seems like the effects of the spell are intended for one creature only and other rulings may be quite unbalanced.