mmm I see your point there, but as a girl that LOVES gender bender fics, it might have to do with the fact, that eventhough we switch the genders it's still hot to think that our boys will look still mannish as women.

It's hot (at least to me it is) to see boys dressed as girls. Don't ask me why it just works for me.

So maybe in an attempt of not loosing that man side of the characters we tend to say that the now girl is hipless or something like that.
Of course it gets worse with AJ, who is skinny as hell and after all there are women who have no hips. Those kind of women that you stare at them from the back and you swear they are men and when they turn around no! they are women.

I don't know if this makes sense or not...
But I do love gender benders. Those are my favorite kind of fics I must admit.