Again, with the lack of understanding about general idea on WHY game developers do this stuff, let me bring a rundown people, please note if you're going to quote with a remark on me being sexist, I suggest you take a hike and go back to Wordpress and dry about it.
On the subject then: Many developers, don't like having female projection avatars in-games (EI: a character we embody as our trophy and record), have their faces bashed in. The thing it is, it's pretty irksome.
The reason Brink doesn't include female characters is because many on the dev-team didn't want characters bashing girls in the face when they're down, they even said so on an interview with Edge magazine, it would be violent, brutal, and do more damage then good to the games image since you know...a guy will be lashing a downed female. Plus, we have to take into account real-life body functions for each sex...I won't get into this because people will quote me out of context.
Gears of War will be an exception to this formula, but remember, you're fighting monsters, non-translatable entities which in no-way-or-form are human, hence they're isn't a human power struggle on sex or idealogy.
I have no idea on why this game would go in this direction to say the truth, but clearly, they're putting females behind as opposed to the front-lines, because last thing they need, is someone crying foul when a huge male golem rips aparts a female spartan...many Wordpressists will have a field day in that.