I think it's a natural tendency to want to keep something that is exploding as far from the face as possible. I really don't think it has to do with their anatomy, but I could be wrong.
fwiw, I notice it on ALL new shooters, not just women. We think women do it more because they typically ARE new shooters. Go look at some experienced females shooters, they don't do this even if they are 'well endowed'.