The two problems with this topic that is going around right now is that:
a) almost no character is "normal". This is true of gay characters and black characters, but also of white male characters. Because it's art, drama, we need to accentuate their characteristics to make them interesting. James Bond is't a regular guy who deals with bad guys and has a steady GF/wife. He's a super-handsome, heroic guy who bangs 1-2 different supermodels each movie. If a character is subtly gay, that's about as exciting as someone who is subtly straight. There are places for it, of course, but most stories like to exaggerate characteristics including sexuality - gay or straight.
b) relatability. When a story is told, interactive or not, you enjoy the story by imagining to some extent that you are in the situation yourself. You save the day, you get the girl...whatever it is. You are the hero. The difference between being attracted to a man or a woman is a pretty big difference to most people. So having a gay hero saving or wooing a man breaks the immersion to most straight men. Romancing a man is simply not interesting to them, so the story becomes uninteresting. This makes it a challenge to write a story when you need to make money and you are going to lose a large portion of your potential audience.
Specifically in games it can be less of an issue when romance has nothing to do with the story and the sexuality of the character can be what ever the player wants to be (Master Chief could be gay). It can also be more of an issue if it is key to the story. The beauty of titles like Mass Effect is that they tailor the story to the player so everyone can have the experience that suits them. In this way, games are ahead and probably always will be ahead of other types of media.
