I think people are overlooking another issue here. Sure, there is laziness, and people might try and make some kind of "boy's club" arguement, and then voice suspicians of the sexual preferances of the development team, however there is a big one:
Fear of socio-political backlash.
Back when City Of Heroes launched City Of Villains and it's "Mastermind" class, there were questions about why there were no female minions. The reason for this as I remember it was started as being the "potential for abuse".
Look at all the videos people make on the internet, all kinds of crude garbage. You start throwing female models out there and inevitably your going to see all kinds of misogynistic stuff being produced, especially when there is a lot of potential to put guns between a girl's legs, or walk around with your pets in tow and bake them in fire, or make a character who sits around "pimping his hoes" to get attention. I'm sure if you think you can come up with things you've already seen along these lines.
I think the question comes down to a game developer looking at their game, and weighing the pros and cons, what can be done with their engine, and the odds of someone coming after them with accusations of creating a misogyny simulator. Also some developers have more guts than others.
The point I'm making here is that this kind of thing apparently fits into the thinking of some game developers. While people will say it's inexcusable for games to NOT have a female character option, due to all of the ones that do, I think they overlook some of the reasons why people might not want to do it.
Speaking entirely for myself, Brink is an over the top, testosterone laden shooter. It's intentionally catering the the absolutly lowest human denominator to begin with. The exact kind of people who would try and lure a female model onto the top of a pointy building or whatever in exactly the right position for it to be lewd, take pictures of it, blow it to pieces with the most gory weapons possible, and post it on Youtube with their commentary. All games are going to see some of this stuff, but Brink by it's very nature might generate more of this given the game's style, and the player base being targeted. You might not agree, but we might very well be looking at a design team acting out of a combination of responsibility and fear of the repercussions. The fact that other game developers have taken risks with similar games and gotten away with it, does not nessicarly mean that other developers want to roll those dice.
I'd also point out that while I don't play it (so am hardly an expert) "Team Fortress 2" is a similar kind of game, which is also targeting a similar demographic. I don't believe ANY of the characters in that game are female either, despite some theories I've heard about The Pyro (who is too androgynous to tell... they might have answered that in the comics, I don't follow it as I said, but again it probably wound't bait the same kind of "satisfaction" given how the model looks). I honestly haven't heard many criticisms of Valve for what is basically the same practice, though as I said, I'm hardly an expert on TF2. With some of the TF2 videos though, I'd imagine if there was a resident hottie "crude" wouldn't even describe the usage the model would be put through by the core audience of that game given what I've already seen.
I know it's not "polite" to talk about core user bases in a negative way, and my intention is not to flame in this case, but to explain thinking. I am well aware of the fact that arguements can be made against everything I said, but my point isn't to say that this is an entirely right and proper thing to do, just that I think it figures into a lot of game generes being dominated by male characters. Also understand that it's not so much about what the players are going to do, but about the attention it generates. If you have 10,000 videos showing up on Youtube of women being molested and killed in various ways by laughing players giving commentary that's going to warrent complaints, not to mention a lot of people deciding they don't want themselves or their kids associated with this, even if the people doing it represent a small portion of the user base... and yes I say "kids", right or wrong, despite the "M" label, game developers very much DO want the youth demographic playing those games as a general rule. The "Dead Space 2" advertising campaign more or less makes that point. I however believe (as an unrelated point) that it's the job of parents to actually control access to the games by minors, not the goverment's. However the more outrageous people are with your game, the more likely that's going to get mum and daddums to actually not buy the game for Junior and that means lost sales.