It's also of note, while folks consider the Social Skills as some sort of verbally-challenged equalizer tool, I do not. The rules are to standardize the resolution of social situations. I don't expect them to be some the Martin Luther King of game rules.
I also find the situation of truly non-social people being drawn to play social PCs as very probable. Possible, yes. It's very possible that undiplomatic jerks who think they are diplomatic will be drawn the class, due to another phenomenon.
But people who KNOW they are socially challenged, I suspect that would be the last class they pick. Just like public speaking is something they avoid. If they happen to help somebody, great. But I would think encouraging somebody to actually speak in chracter in front of a small group of his friends would be far more helpful than some rules to let him avoid facing the problem.
That makes me sound like a big meany or something, but my point is, consider the rules from a matter of getting consistent and fair arbitration of social encounters from your GM, regardless of whether he is in actor or narrator head-space. GMs do get biased, and players can't read their minds to know what was fair. Systemetizing the process was an attempt to clean that up.
You would be wrong in thinking that socially challenged people never have a desire to try and play a more socially out going character. Part of the fun of role playing is playing against type.
You brought up a point that I agree with, social skill rolls takes it out of the hands of the DM and while I am a big believer in DM control and trusting your DM having a roll can be the fairest way to adjudicate it. I have seen issues in older versions of the game where someone gave a great speech and the DM said no it didn't work and players feel picked on and railroaded.