I'm a strong supporter of the notion that men and women cannot be close friends.
Or rather, I think if they are friends, at least one person in that relationship is settling for 'well if I can't be their partner then at least I can be their friend...' and it's most commonly the man. The only exception to this would be couples who are friends, which is an entirely different ball game. You're not friends with the individual then, you're friends with 'Rick and Mandy' or 'Sue and Joe'.
I think guys are far more likely to stick around a girl they fancy and pretend to be friends. I'm not sure what girls truly believe that none of their male friends fancy them - I've had male 'friends' before and I always knew when there was something more there that they just weren't talking about, more often than not because I had a boyfriend.
Most guys I know just don't bother to hang around with girls as friends unless there's at least a minor attraction there. And hey, I think most women over a certain age wouldn't either - the exception being the cruelest of the species, the teenage girl. They like the attention and they're not quite mature enough to understand how hurtful it can be to their male 'friends'. How many relationship forum posts are by teenage boys asking why they're stuck in their friendzone?