I think the idea that women are less capable is an interesting one. I think that the fact that there are women in the top positions (not all of whom got to those positions because of things like affirmative action, surely) says women are at least reasonably capable. I think that it is more a social factor, as in I think women are generally socialized in our society in a way that doesn't foster that kind of ambition or instill the skills and knowledge to achieve such goals. So, maybe they aren't capable because they aren't properly prepared... but that isn't necessarily something inherent in the gender, if that makes sense.