It's probably not a whole lot fewer girls than would be comfortable dating any other given person, male or female.

I hate to make statements about an entire group - but women over-all seem more comfortable with variant gender. I would guess it's just the culture - where women are told that it's "what's inside" that matters more than we generally pound that idea into guys since our culture likes to think and perpetuate an (incorrect) idea men are less emotionally capable than women.

*shrug*