My best friend is a female. She was the best "man" at my wedding.
She's attractive and has HUGE breasts and I've wanted to sleep with her since 1989, but it hasn't affected our friendship. I'm pretty sure she knows I want her, mostly because I make lewd comments along those lines all the time to both her and her husband.
Maybe it works because she's like a guy in that she has a potty mouth and watches sports, but we also have similar taste in music and movies and she's hilarious.
I actually have more female friends than male ones (on the West Coast anyway), so obviously I think guys can definitely be friends with a female. I think a lot of guys are just encountering the wrong ones.