Straights and homosexuals (gays and lesbians), would disagree with you. lol
I personally think there are very few, long-term bis (or pansexual if you prefer). I think they are as rare as asexuals. Eventually many bisexuals gravitate towards same-sex attraction.
I agree with you about bi-curious though (sorry Allie). It doesn't make sense to me. If someone is curious about the opposite sex, why don't they just try it so they will know? "Bi-curious" is really just another word for "same-sex fantasy", and a fantasy does not indicate an actual sexual preference. So maybe the people who say they are bi-curious would rather remain in the fantasy stage rather than find out they are turned off when they enact their fantasies?