I usually don't chime in on romance threads but my opinion is that it makes sense that characters are more defined. Some people are straight, some gay/lesbian and some bisexual. I just think it would be weird to have a LI companion act one way with a male romance PC but then act the same way with a female romance PC. Unless "in game" the LI character declare's him/her self bisexual it makes the replays weird. It also breaks continuity with the characters.
Don't shoot but take ME3's James Vega, (I know he's not a LI but think of his "character") he states he doesn't "swing" that way, even if he didn't state that I find that it would break my sense of his character if he was straight with my Femshep but then gay for my Manshep.
On the other hand Izzy is Bi and states it, Fenris it "fits" his character and the interactions that he could be Bi, Anders on the other hand made no sense all of a sudden he was Bi or Gay. As much as people might want it if you think in "character" then not everyone should be able to be a LI to every gender PC.