My opinion: There are a LOT more bisexuals than people would think. I honestly think Kinsey was onto something with sexuality being fluid. Right now, most people would not be as forthcoming on being bi because they have a CHOICE. We know being gay is hard in today's society, so why would a bi person CHOOSE to go down the gay (harder) path when they can easily just be with the opposite sex? I mean, why even bother wanting to meet gay people of your sex? You might end up falling in love with one of them, then you have a hard choice to make: be with the one you currently love and lead the harder life, or try to forget about him/her and attempt to find someone else of the opposite sex where it IS possible to fall in love with him/her too. So I think a lot of people don't even want to touch the waters unless: it's in a safe environment (fooling around with friends who you're attracted to but know that nothing serious will ever happen) or it's in an environment where you're forced (physically, mentally, emotionally) to go for the same sex. Such as accidentally falling for the same sex, being in prison, or losing your trust in the opposite sex (bad break ups, rape, etc).
This theory of mine explains everything in Berry''s post (#69).
It also explains why it "appears" that more and more people are "bicurious" or having that "lesbian experience". A lot of people blame it on society becoming immoral. To me, it's just because there are a lot more safe environments than ever before.