Boys that Play Girls that Play Games

I am, quite honestly, at the point in my MMO life where I assume that any female character on screen is probably a male on the other side. And it no longer comes as any surprise to me when I see polls supporting this theory. However, what does continue to puzzle me is why players do this. I've played both male and female avatars in the past, but something about the pronouns always leaves me a feeling bit confused when trying to play the other side. This article suggests that it's just "pure MMO capitalism," with people simply playing to the advantage of being a pretty girl. I'm open to other ideas, though - why do you play a character of the opposite gender?