You're missing the fact that the 'xbox live' community represents the overwhelming majority of the gamersphere. Because I'm assuming you're lumping in the WoW, CoD, BF communities and so forth. The big ones. Having vacationed in those communities from time to time I can tell you one thing for certain: homosexuals don't get a lot of positive talk. In fact one of the number one insults that crop up time and again are homosexual pejoratives.
Homosexuals are having a tough time right now (which is nothing new). Did you see the lines of people outside Chik-fil-A's lately, queuing up to show their support for the oppression of their civil liberties? Can you imagine what that would feel like if it was tens of thousands of people all showing their solidarity in declaring you, Prof. Beany, a sub-person?
Let them have a gaming convention. Let them have something tailored to them, celebrating them, a place where they know they can be open about themselves and be surrounded by those who are like them. A safe place where they don't have to worry about maybe being harassed and accosted, someplace where they can feel like it's for them.
It's true that cons like PAX don't necessarily discriminate, but that doesn't mean that subsets of people can't have one that's for them. And just in case you're worried about it being some sort of reverse discrimination, you're welcome to attend to.
In fact, it's sort of the flipside, isn't it? I mean lets face it: what with booth babes and such, it's pretty clear that video games are marketed largely to heterosexuals (and being the overwhelming societal majority that's no surprise). Homosexuals are welcome to attend, but it's not for them. You (and the rest of us really) are so used to having things catered to us, for us, that it can be nigh-on impossible to imagine what it might be like if it wasn't. Well, a con like this gives them a place where in some small way, it will be.
Are they not allowed that little bit? That tiny thing, without the rest of us 'enlightened' folks trying to cut them down?