Mar 12th 2012 9:35AM You can never really count on stereotypes with wow. It is like saying, "Guys like pvp girls don't." Well, every Friday I group up with four other people for BGs and three of them are women.
Now, I'll say I've met far fewer female tanks than female healers, but I would wager that is because more men still play the game. I have a good friend (one of the pvpers) who was a tank before she became annoyed with druid tanking in cata, but who tanked in BC and Wrath. My wife is working on her tank, but does not have a dedicated healer at all.
I am just now rolling my first tank, but I've healed since vanilla, and my girlfriend at the time rolled a rogue.
This is one of those generalizations that tugs at the social stereotypes already ingrained, so to see it pushed onto wow is not surprising, but it'll become more apparent how silly it is as the digital generation makes themselves known. Your middle school and high school girls now play MW3 with each other and with their male friends (possibly their boyfriends as well). It really is only a matter of time before you'll get a situation where you won't know at all what the gender is of the person you're pugging with due to statistical likelihood.