You say you don't need discrimination to explain it, but your explanation assumes discrimination ie. you have to be really damn good in order to even have a chance as a woman. There is another explanation, the distribution of IQ between men and women:
> Another factor affecting perception may be distribution of IQ ... Although [men and women] are on average the same, the people at the very top and the very bottom of the IQ bell curve are more likely to be men. That is a pattern that we see in the university setting, with men either being at the very top of the class or at the bottom.