Forgive my generalizations, but women are taught from a very young age to be compliant. Neat. Quiet. Courteous. Don't make a scene. Don't draw any attention to yourself. It's just easier to be passive because that's what we're told to do from a very young age. It's a pervasive historical stereotype, and you'll be hard pressed to convince me that it has disappeared in our society. As an example, just look at how many women are terrified of asking a man out because it's not "proper."

Do remember that there is some component that is genetic (or rather hormonal, which is merely initiated by genes and may be altered) - testosterone is definitely related to both aggression and muscle growth, and is likely related to the way the brain track objects. In lower animals, estrogen will actually force the females to submit to copulation.

That said, I agree that the societal effects predominate in humans. But while it hasn't disappeared (and likely won't ever completely), it is significantly decreasing, and in Western society isn't enforced by law.

I posit that women are more likely to condemn themselves (and perhaps each other) than men are to condemn them. In my personal experience, men tend to respond very favorably to women who act definitively.