Here's what I believe about bisexuality: That anyone can be bi, however, not everyone is.
I don't think that one can completely sit and say, "Well, this group of people can't be bi because of their gender/race/nationalit y/etc", since I'm sure that there are bi people in just about every group that you can come across.
And as for the second bit, I don't think that one can say the opposite: "Okay, well, these people are bi because of their gender/race/nationalit y/etc" for just about the same reason, that there will always be people in these groups that defy the over-generalization (the reason why I bring this up is because I've heard many argue that "No matter what, every woman is bi" or something along those lines, and I feel that's simply not true (insert whatever difference that people have where 'woman' is, but that's just the example I heard). This thread reminded me of that, so I included it since it seemed relevant, lol)
But that's just my opinion
P.s: Don't feel bad, all, I didn't know DeliciousSurprise was joking either, lol. It took me a minute to figure out that she was