I heard a statistic on the MMO report that said 3/5 WoW avatars are female, but only 1/5 WoW gamers are female. That means that for every five players in WoW, 2 have some Freudian issues going on. More seriously though, I think it is a psychological thing, does your avatar exist for you to see, or for others to see in your mind? If your a straight guy, and you think the visual representation of your character is there just for you, it's actually more logical to just go for eye candy, whereas if you want other people to be able to draw some conclusion about you based on your avatar, it would make a lot more sense to have a hulking, awesome, super-hero for your character.