As Border House points out, this isn't just WoW's problem. Fantasy and sci-fi in general have been the domain of boys in the past (even if that is changing quickly), and the sexual depictions in the genre have reflected that, for both traditional and financial reasons. As I pointed out the other day, all of Blizzard's luminaries thus far have been men -- is it any surprise that the game is designed from a mostly male perspective? And as BH also says, fortunately, WoW has lots of different gear. If you don't like what your character is wearing, then you can find something else.
Is this an issue, then? For this game, at this time, probably not. Most players of the game realize that not only do people not walk around every day wearing plate armor and wielding magical swords, but that most real-life people don't try or have the interest in living up to any weird expectations of sexuality placed on them by a fantasy character. Not to mention that these are not characters necessarily, but avatars of ourselves -- some women would rather wear the "plate mail bikini" for fun than feel objectified and exposed by doing so.
Does it mean that we'll never have a game that realistically portrays the people playing it, or a fantasy game where the men are as exposed and sexualized as the women? I don't believe so -- as the primary audience for both the fantasy genre and videogames in general changes, I believe we'll see more games and instances where these traditions are subverted, where our heroes aren't manly men or sexy women, but real, actual people of all shapes and sizes.
But let's be honest: just as some men have their traditional genres where depictions are skewed, so also do some women. And as long as people continue to support and invest in those genres and their conventions (and why wouldn't they? It's fun wearing crazy armor and killing bad guys!), they'll be around in this form for a long time.