I agree with RxnMan, but wanted to add that I also believe it has to do with how women were raised, and what they actually like to do. The whole "women are inferior" is a socially constructed notion derived from god knows when. As RxnMan said, the higher ups who view the world in this manner are retiring away, thus slowly removing such kinds of discrimination from the playing field.
However we must also factor in family, and personal preferences/goals. I wouldn't appreciate science so much if it wasn't for my parents. Often times, girls and boys are brought up differently. Although in modern times, there are rarely any boundries in what kids are taught as children, there are probably still some kind of differentiation. A good example would be my friend, who's dad is an engineer, and who's mom is a teacher. She is close to her mom, and thus wants to be a teacher. She totally dislikes the engineering way of thinking... "always have to be quantified (too analytical apparently)".
Another factor would be goals. To some extent, I have known both men and women to want to have a family. Some of my female friends at some point want to take a step back from work/school, to raise a family. They want to be there as their children grow up, rather than be busy in the lab, office, or classroom while their kids are raised by a babysitter (just an example). Conversely, I have some friends who are willing to push hard with their career goals, but accomplish their familial goals by having a supportive spouse, or other family members (mom/dad?). Ultimately, its what they want, and how they do it that defines how far they will go these days.
I whole heartedly think think that the discrimination factor is less significant these days. A good example would be our med school. Our dean for the med school is a woman, and she also doubles as vice chancellor for the entire university. More recently, we have appointed a female CEO for our medical center. Over the past 6 years, I have interacted with numerous female associate professor/full professors in our school of medicine (mainly MD's). So they are certainly not under-represented in terms of actual ethnic minorities. Relative to gender, I must admit there are still probably more men, but it is probably along the lines of 55-60% men, so its not that bad. I don't care what the ratio is, but aslong as people are happy and good at what they do.