I would think that bi-sexual is just a term that means you're OK with having sex with either gender. If you have romantic feelings for the opposite sex, that would potentially make you gay. You can be bi-sexual without being gay.
For the purposes of this site, what people are mainly looking for from this sort of classification is whether someone will engange in any sort of sex with you, or not. While it's possible, I suspect most are not looking for or caring about whether you have romantic feelings for someone or not.
So if you are willing to have sex with either gender and aren't listing yourself as Bi because you don't have "romantic feelings" for the opposite sex. it's no biggie, but you are probably missing out on play time opportunities.

