I agree most of us have the potential to be bi but a much smaller proportion of that group is likely to be. Every person has a certain amount of male associated traits, and female ones, in varying strengths. In my opinion the most balanced people have near equal amounts of both; guys who are totally butch are missing something in the same way totally feminine frivalous girls are. Those 2 extremes need each other (male/female; yin/yang) to be complete as a couple and fill each other in a bit (although they will never understand each other) and are therefore much less likely to be drawn to the same sex.
Bi-curious just shows they have a mind and a sex drive.
Bi-sexual can show they have a taste for what they love in themselves. My first experience with a woman was pretty mind-blowing for me - it was a revelation as to what it was that guys liked in us girls - soft skin; the breathing, sighs, and moans; gentle kissing; the soothing comfort of breasts; the pleasure of yielding. I beleive I've evolved into a better lover than I would have been without that experience. Society has made girl-girl love much more accessible and therefore less threatening than the male equivalent.
Gay is a slightly different scenario again. I recently saw Brokeback Mountain and found it deeply moving...