Triple A titles for the consoles are generally aimed towards a specific demographic. Granted, that demographic relies heavily on the type of game and console. For all intents and purposes, we will talk about the "Shooter" genres; as RPG's usually dont apply to the standard demographic, and usually have customization of some sort. The shooter genre is aimed towards High School/College Male, the one that spends an average day at the gym and talking about how sick their quickscope was.
When it comes to marketing, this demographic doesnt want a human character with flaws and emotional issues. They want one bad-ass no-face motha-fucka to blow the shit outta the genocidal aliens. Most of the time, they arent doing it for love. They are doing it for vengence, or because they just wanna kill some aliens. Now, there are exceptions. First off, there are a few games that do have females in them as leads/major characters. However, I would like to point to games like Tomb Raider and point out that if you DONT think those games are selling because of some sort of sex appeal, your out of it. Second, games like Gears of War, probably one of my favorites shooters, mixes this up a little: the characters do have their own personalities (although most can be described by grunting and pointing to a PlayBoy magazine), there are motivations (hence why Dom whines about his wife every 4 seconds), and they will be adding something to the genre by including females into the mix (and I think its hard to be sexy when your wearing a half ton of armor; a rule that applies to everything).
That being said, the AAA games industrys are all about marketing towards a key demographic. Most have hopped onboard with shooters or Sandboxs, which have their own niche appeal to the, well, guys. Casual games aim towards kids and the elderly, Nintendo makes games friendly for kids, but appealing to other crowds. RPG's appeal to, well, RPG fans (we are kind of unique), with the split between JRPG fans (who have their own demographic qualities) and WRPG fans (who also have their own demographic qualities aka OMGOD BIOWARE).
Would it be refreshing to see a game where the lead was a female? Yes. Would it be refreshing if she was a likeable character instead of a cold-hardass who looks like a model with two watermellons struggling to leap out of her shirt? Yes. Would it be refreshing to see a female lead pull a game, and do it without it feeling like a gimmick or like its trying to market off of sex appeal? Of course. Unfortunately, thats just not something game developers are looking into. I think it would be FANTASTIC if the lead in the new Call of Duty was a female, but the way things are in this industry, it probably wont happen.