I'm really not sure whether girls with Asperger's are on average any better looking than boys are. I mean simply because there are a couple of pretty ladies posting pictures on here does not make this representative at all.
I mean, just generally, women seem more concerned with looking good in photos which are posted online than guys do. Of course, I might be wrong here, but that's just what it looks like to me. On here, on facebook, on pretty much every (social) interenet space I've ever been on. So, maybe it's simply that ladies try much harder to look hot or cute (whatever they may be either consciously or unconsciously aiming at) in the pictures they post than guys do. "Aww, you're really pretty, cute, etc." still is a rather important compliment for a lot of girls, at least when their being honest about it. That seems to be less a case with guys. Might have a lot to do with how we were brought up and how society still conditions girls to lay a lot of focus on looks (in themselves, as well as in others of the same (and possibly other) gender) and guys to focus more on abilities and skills (in themselves, as well as in other of the same gender). Sure, this is not an exclusive truth, it's merely an observation cencerning tendencies that are definitely there.
Thus, I'd argue that looks might actually be fairly evenly distributed among girls and boys who are (actually) on the spectrum. Girls might just be more selective in the photographs they keep, post on line resp. aim at displaying some very specific image (be it nerdy-cute, hot, shy-hot-cute, whatever) in photographs they consider showing who they really are resp. who they want to show to world via the interwebs.
Anyhow, that's just my two cents and I know that this is by no means true for all girls (women) resp. guys (men), but even with quite a few Asperger women on here it seems to be an issue/tendency.