No. 90% of the time it's because they're desperate to get ANYTHING.
I actually don't perceive gender as anything but a word. Never have, since I discoveredthat how I'd been conditioned to think of homosexuality was wrong and that I should stop feeling guilty that I had a massive crush on my best friend at school.
Turns out he was straight though. Which sucks. :( And then I had a relationship with a guy who couldn't make up his mind whether he was straight or bi or gay, and so that's out the window because he kept begging for sex then saying he was straight and didn't want it any more afterwards... each damned time...
I've had relationships with women before. Two of them (not at the same time of course. That's just being unfaithful. o.O ) and one even lasted 8 years. But then she wanted a collection of guys, I just wanted a monogamous relationship. -.-;
I used to tend to get screwed over a lot. Then again I have since realised that I no longer need a relationship to validate my existance. I can be pretty much happy on my own, single. :)