In the case of sexuality, it is likely that we each exist on a continuum that runs from strictly gay to strictly straight. And it is clear that most people are towards one end or the other, though there is clearly a range, and for some people, sexual identity is more fluid than for others. This may be more true for women than men. (The biology of physical arousal is really different in women than men as well... something that's only recently become apparent as people are finally using female subjects. Women are not men.)
The number of people who are overtly gay (as in, actively homosexual) is lower than the number who have a potential for homosexual behavior without acting on it (Hence the 2% vs 10% discrepancy). Interestingly, a substantial fraction of men who have sex with other men insist they are heterosexual.
The absolute middle position would be truly bisexual; the ones who do have a more conscious choice. Let me make a point here: many people opposed to gay-rights have a profound misunderstanding about bisexuality, thinking that bisexuals want simultaneous sexual partners ("threesomes"). This is NOT the case; a bisexual is simply someone who can orient their affections to either gender. If you have ever heard a man say, "I prefer redheads and blondes," that doesn't mean he expects to sleep with them both at the same time. It means he's likely to date either a red-head or a blonde, and not likely to be attracted to an olive-skinned brunette. Similarly, a bisexual may happily and monogamously date or marry a man or a woman. It's simply that their next date may be with someone of a different gender.
We see a range, or continuum in other traits too. Let's go back to handedness. Most of us are right handed, but it's a rare right handed person who can't do a few things with their left hand. For example, I'm right handed, but I can pour liquid from a container using either hand pretty well. And, some people are truly, completely ambidextrous and can use either hand interchangeably. (So the folks studying handedness don't use "right" and "left". They use "right" and "non-right".)
The majority of people who identify as gay or lesbian feel themselves oriented towards a person of the same gender, and not making a conscious choice. After all, given the stigma that ranges from social disapproval in our society, to imprisonment, torture and execution of gays in some fundamentalist cultures, it is not clear why anyone would "choose" to be gay.
People can suppress their orientation, and try to "pass" as straight. We certainly all know of men and women who entered a straight marriage, had children, and tried to maintain a hetero life before finally admitting that wasn't who they are. In the past this led to a lot of misery (think of Larry Craig toe-tapping in the airport men's room, or conservative and anti-gay California legislator Roy Ashburn cruising gay bars). In our more enlightened age, young gays can grow up without trying to pretend and can be honest about their sexuality.
To read this entire series in order, visit the Genetics Page.