Alright. I opened my big mouth, so now I gotta give my theories.
I've heard people before say that more male's transition to females than the other way around, although I don't think I've heard any sort of scientific sort of survey. You hear more about crossdressers that are male than female. And the survey about what body androgynes are on this forum has suggested that there are more males than females. So, I have always had theories about this. Completely unfounded hypothetical ideas. They may be completely wrong, and you can eat me alive if you think I am completely off base.
For a guy to dress as a girl and look like a girl, he has to do some pretty serious stuff. Bra stuffing, lots of makeup, shaving. And if people find out she's actually a guy, well, then bad things happen. Everyone will call him gay, regardless of his actual orientation. Gay might be hip right now, but that tends to break down when a guy says "Hey that chick is hot, oh wait, that's not a chick."
For girls, it's a tad easier to dress as a guy. Yes, if you have larger than A sized breasts you have to bind (or wear something really baggy). But wearing guy clothes helps you blend in fairly easily, and if someone realizes you are a girl in guy clothes, they don't really think it's THAT odd.
I know those are generalizations. but... Most folks think girls look good in a tuxedo, most folks think a guy in a prom dress is not normal. I don't know how many posters and calenders there are out there of girls wearing guy clothes in sexy ways (firewomen, policewomen, lab coats, etc... yes I realize those clothes are not gendered, but society still tends to think of them as 'guy clothes' even though they really aren't any more). There aren't that many calenders out there of guys in dresses (although there are some, and they are usually quite awesome IMHO).
So basically what I am saying is that I think that society makes it more okay for girls to be guys, but not so okay for guys to be girls. So that means quite of few of the gals out there don't even realize what they are, or don't think about it so hard, or can come to terms with it easier. But the guys, well, it's harder because society really beats on you. So you gotta go somewhere to look for folks to talk to.
So this would affect andros even more since it's easier for a girl to be a 'non' or a 'both', but much harder in society for a guy.
My other theory, which is even less of anything... I don't even believe it myself, but hey, I can have a theory I don't believe, right? Anyways... As unborns humans are more similar to females than males. So maybe it's more natural to be a female than to be a male?
And the last one, which I just thought up while I was typing this all... We were all born from women, and shared blood/food/hormones with our mothers before we were born. So maybe if there were people that were born from males then it all would be flipped around?
I dunno. Maybe I'm completely wrong. If nothing else, I bet this will spark an interesting conversation.