I only require it if I can't figure out how or why something would work.
Yeah, I may have come across as more opposing of the concept than I am, and it is definitely a very tricky line - partly because PCs do end up with these absurd capabilities that far outclass anything we can imagine someone doing in real life.
Social situations are the classic dilemma - if the player of a bard walks up to a bandit leader, calls him a punk, and then claims he's using Diplomacy to make the guy worship him because he rolled a 50, that's rather obnoxious. But it is also isn't cool to have the soft-spoken player with a character heavily invested in being diplomatic always have to take backseat to the Cha 8 dwarven fighter... whose player is a smooth talker.
There is no easy answer... but at the same time, I definitely recommend thinking things through before putting the burden so squarely on the player. If something genuinely doesn't make sense to you, that's fine, and the line will fall differently for everyone... but yeah, I've seen DMs who have abused this viewpoint in the past, and they were the worst DMs I've ever had.
The other side of the 'don't make people explain things, just let them use their abilities" position is that its absolutely worthless when your players want to accomplish something that isn't actually an ability or in the rules. Like, say, disguising yourself or forging a document, yesterday before this preview article was published.
Now that is absolutely not true, and I will completely disagree here. Not requiring players to supply their assumed character's capabilities in no way means you cannot reward players when they do offer creative solutions or ideas that may take advantage of their skills in a clever way.
And, again, the presence of listed rules that let players make exceptional use of their skills with the proper training does not mean that those skills cannot still be used in their normal fashion, or still be used creatively in the right circumstances.
That's a nice theory, but it doesn't really apply. The PHB doesn't mention anything about disguising yourself that I can remember. Certainly nothing in the Bluff entry. It would seem that the only official way to disguise yourself is with this training, or with magic. Likewise I can't seem to find any "regular" way to forge a document.
Those facts notwithstanding, I've been allowing this kind of thing with skill checks. I don't really feel that disallowing it and requiring a feat to accomplish the same thing is increasing value.
I'm not sure how you read these rules as saying Bluff can't be used for disguises or forgery separate from this. This give specific rules on doing such things in an exceptional fashion - I think you are making several jumps in logic to conclude it removes all ability to use your skills outside of it.
I'll try to look up page references when I get a spare moment, but don't have the time now - that said, if you genuinely feel the listed abilities here remove existing capabilities, I think we simply have a disagreement of viewpoint on how the rules are presented that isn't likely to be easily resolved.