"Bi now gay later"?

The expression "bi now gay later" was a favorite of a friend of mine during high school. Now science backs this up. But what doesn't make sense in the study cited in the Times is this: if 1/3 of all men--self-identified as gay, straight, or bi--didn't get aroused by any of the porn they were shown, how can that not affect the findings? Wouldn't it make sense that bisexuals might be just the sort of people who'd be turned on by unconventional things, who'd find two Abercrombie guys or two Britney Spears clones going at it less than exciting? Or who are turned on by specific people in specific situations, thus rendering gender less important?

I don't doubt that many men go through "bi" phases before taking the other foot out of the closet, but to say that all bisexuals are simply imagining their preferences doesn't ring true, and doesn't sound as if it was proven true either.