Could it be, there's less women in programming because it's just starting to rise as someplace they're needed? Or as something just now becoming 'visible' enough to get their attention?

It could be something that starts out much earlier in life. I got into computers very early. The only person in my class at the time that cared for them was also a male. Even still, the act of programming itself just doesn't draw many people early on - which for the most part is why we currently have programmers. They got interested early.

Lawyers, Doctors - those are things that can be decided late in school. 'Hey, I think i'll go to school for this now'. Programming just doesn't have that draw - or didn't. Perhaps now that it does, we'll see far more females in the programming workforce in 4 years time.