Somebody pointed out that we started seeing a lot more left-handedness after people stopped thinking it was devilry. I think sexuality has always been a spectrum, but we just suppressed the "abnormal" and no matter where you were on the spectrum, you pretty much needed to decide if you were going to be a totally straight person or be a gay person (unhappily closeted or alienated but out of the closet).
I think the younger generation is far more comfortable accepting that sexuality is a spectrum. Kids will say they are Q probably because it gets them attention, but also because they really are open and it can simply be an admission that they don't know what they are yet.