Having them allows you to cater both to verbose players who love to talk, and to quiet players who are not as comfortable and skilled at roleplaying, or who aren't as confident or gregarious as others at the table. Not having them caters to the former and punishes the latter.
All in all, I think it's best to have them there as an option at least, even if the DM allows good roleplaying to strongly affect or even subsitute for the statistic.
A player with a PC in combat may suck at tactics, but he can ALWAYS fall back on the roll of the die & the combat rules to help bail him out*. A player in a RPG without a system for simulating social skills has no such safety net.
I mean, I know jack all about the practice of martial arts beyond what media (movies, documentaries, books, comics, etc.) and a single day in a karate class have taught me, but I can still play a really cool martial artist in most game systems. Were combat handled the way some treat social skills, I'd be limited to playing brainy wallflowers with artistic talent.
* unless there's some RPG out there that bases combat results entirely upon what players actually know about combat.
The outcome of social skills is much less so.
For example: I have just intimidated someone do they run away? Do they surrender allowing me to dictate their actions for a period of time? Do they seek to run away? If the outcome were a little more fixed and anything outside of the basic set of outcomes resolved by role playing or fiat I would be happier with the rules.
There was an analogy that Monte used in the transcripts about social skills that sounds kinda like common-sense at first, but I think falls apart upon closer scrutiny. It was something along the lines of "we don't expect players to come to the table knowing how to use a sword, so why do expect that of social skills?"
Hell you don't have to give the worlds most perfect lie to bluff the guard, just TRY. Effort is rewarded.
A player with a PC in combat may suck at tactics, but he can ALWAYS fall back on the roll of the die & the combat rules to help bail him out*. A player in a RPG without a system for simulating social skills has no such safety net.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.