I'm here to tell you that's not true. I play a resto shaman who heals like a madman (and a shadow priest, although I'm not sure if that counts or not), and while there are some female gamers who play priests and druids in my guilds, the majority of priests are actually guys. In fact, I've played with a surprising (to me) number of women warriors. There's nothing an old-school gamer like me loves hearing more than a female player complaining because the guild is pressuring her to spec out of fury and start tanking. Just more proof that videogaming is a girl thing, too.
Sexism aside (of course there are exceptions to every rule), Garthar can't be right, can he? There's no way only women play healers. Is healing as a class more feminine somehow then smashing things over the head with a large weapon? And where do the other classes fall in here? I know a few women that play mages (and play them well), but I have to admit that most of the rogues I know are played by guys. Does our gender have any say at all in what classes we choose to play?