Now my two cents on why more women don't train -- it's called LIFE. There is dinner to be made, kids to help out with homework, running the kids to soccer practice, PTA Meetings, etc etc etc. We are so used to nurturing others, that we do not take the time to nurture our selves. I think it is hilarious that I equate nurturing to being thrown around on the mat by some big blokes!
I think that this is one of the main two reasons why more people in general don't train -- aikido or any other martial art requires a lot of time. People will take a month-long or six-weeks intro class and train a couple nights a week, but when they think about giving up a couple evenings of every week indefinitely, it's a different matter -- they can make that time on a short-term basis, but don't want to do it permanently. And, as you say, in a family situation, even today a woman is likely to have a larger percentage of the child-care/family-care responsibilities (whether pressed on her or assumed), which would leave her with less time to train.