I think the issue is that in so many games we assume that characters in games are not LGBT unless explicitly stated. How many characters could be gay, lesbian or transgender and we never know about it because, just like in real life, there are other things going on and it doesn't really come up.
Seriously, try it, next time you're off on a romp to save the world/galaxy/universe from terrorists/demons/orcs/orkz/monsters/evil/good assume that any character that doesn't give you any reason to think otherwise is LGBT and see how much difference it makes. Turns out it's very little.
Also as a sidenote I like how offhand Mass Effect 3 is about some of the character's sexualities. Casual mention of a guy's husband, inviting someone to bed only to discover she's a lesbian. Very classy.