Maybe I have more time to cycle and post as I've no kids? (I also commuted in London for years, partly because I worked shifts which didn't fit well with public transport.)
You see a similar profile with walkers- women disappear in their 30's, but come back later on. When the kids are small, it seems that in most cases it's still the ladies who do the short walks with the kids while the men still go out walking the big hills with their mates fairly regularly. I suspect it is worse in cycling, because as fewer women do it, then if you're not the type that likes to cycle alone as I do, it's a bit more lonely getting fit again if you come back to it when you're older. People wouldn't want to join a group unless they felt they could 'keep up'.
I notice that in families with kids, again on the whole and no disrespect to any of the fine men on here, men seem to feel more able to justify spending money on personal gear. I'm not saying men are to blame for this, just that it's what I observe- women in cheap boots and waterproofs caring a nasty, uncomfortable rucksack with all the food in, trying to keep up with blokes in state-of-the-art gear who have never had a break in their training carrying a top-notch rucksack with an expensive camera in it and GPS gear....
I can't complain, as I have the most expensive bike in the house, (two adult males included) and the camera gear is mine, ALL MINE...
I don't do the laundry or the washing-up either- I must be turning into a man.
I can say that at work there are about 6 ladies and 2 men cycling regularly, I'm the only one on here though, ther is another lady who reads the forum but does'nt cycle due to location from home. there are probably another 2 ladies and 2 men who cycle but infrequently. I certainly see more males than females out on bikes commuting. Sorry I know it's a little bit off thread, but thought the numbers might be interesting. 
