Ahhh, there is the word I was looking for. "Characterization".
I have to admit, I tend to think that role playing and characterization go hand in hand. But, CJ, you do make a darn good argument.
Let me try to take a slightly different stab at the beast. If I watch someone play their character for a session or two, I should be able to pick up that character sheet and there should be no surprises, IMO. If the player is playing a highly intelligent, tactical character, then I should see a decent Int score on that character.
Let's say that a year ago, I would have agreed with you. That a 10 CHA character doesn't try to be Face.
Reconsideration of the topic and the factors involved and the people I've known and met contradict that.
a) i've already stated in the other thread that real-world skill bleed-over is hard to block (talk player is more likely to be a talky PC).
b) just because somebody THINKS they are good at something doesn't mean they are. In fact studies have shown an inverse relationship. Ignorant people think more highly of their ability (when they actually suck), and vice versa. So you're 6 CHA PC is MORE likely to be trying to act all suave and stuff and always be turning others off (and not know why).
c) since D&D is interfacing verbally with your GM, your GM still gets to apply your stat to the actual outcome. Your stat is the final gate-keeper to success. This models how real people behave in ways that they TRY to impress or ways that they play it down and the former can fail at it because of charisma they lack, the latter succeeds because they are very charismatic.
d) 10 CHA is not so awful that you can't attempt to be charming. We all do it and eventually we all get laid. You might strike out a lot however... 10.5 is the statistical average and it would be disingenuous to assume it means we are all uncouth spazzes who could never convince anybody of anytng like buying our car in the driveway. higher levels of CHA are what get you elected to political office or get a following for your band or cult.
e) Real smart people do dumb things like get addicted to coke and become coke-whores (true story). The number on the sheet does have mechanical impact on abilities in the game. However, that doesn't mean that in all things they make smart choices. Just like in real life. Vice versa, there are dumb people who manage to not make any fatal mistakes and pay their rent, etc. They still suck at math and such.
f) D&D is a game for smart people, by smart people. A large part of playing it is learning strategic knowledge and applying it to subsequent characters. As such, the player only makes a mistake once. Subsequent PCs never make certain mistakes. Nobody wants to play old school and roll up a 4INT PC and be forced to play him so stupid he gets the party killed. So there has always been some bleed-over of the real-world player into the PC. We are not fully acting AS our PC as written, though we may try to.
anyway, that be a summation of reasons I see. And by all means, I play my lower CHA half-orc Barbarian as much less verbal and nuanced than my other PCs with higher charisma.
I simply see that there can be other ways to interpret the stat as compared to the player's behavior.