The ratio is asshat is directly related to the size of the userbase. If WoW was a less popular MMO I'm sure there'd be a lot less idiots, too.
But since it DOES have 8 million users every anti-social 20 something year old plays along with their 9 year old little brother, their 45-something uncle and his 32-year-old fiance. Their thuglife 16 year old neighbor with his tall T and Tupac CD, his "kind skanky, but kinda hot for a whitegirl and that short skirt is really helping her anyway. I don't need to pay attention to her personality, I'd just hit it and quit it" girlfriend, and even her dog has a level 23 pally on Arthas.
Point being: I went to a LAN cafe and there was an 8 year old who just had his parents buy him a level 60 NE druid on eBay...WoW's demographic is ridiculous.
(Note: Almost all the scenerios, save for the dog, are based on real-life examples I've ran into...most of the ages were made up on the fly, but my 9 year old cousin does have a troll hunter.)