Aye, I recall reading an article about how young men were more likely to want serious involvements than the women they were seeing, but I can't recall where the article was from.
Anecdotally, my female friends tell me that in their casual sexual relationships with men (not one-night stands) it has for them been inevitable that the guy starts to develop inappropriate feelings.
I think the comment on gay men is telling, and might shed some light back onto the hetero stereotype. Put simply, promiscuous (and/or camp) gay men are the most highly visible ones, leading to a stereotype that all gay men are promiscuous, while in reality you're probably surrounded by plenty of gay men who you just assume are straight - because they're not like what gay people are supposed to be like. It's a self-confirming stereotype.