I've been trying to define why people are so attached to gender stereotypes and the whole discourse of the so-called male/female differences. It is self-evident that we will never be able to discover any gender differences that would transcend cultural, religious, linguistic, social, racial, class, educational, etc. divisions. As hard as we might try, we will never manage to prove that all women (or men) on the planet share anything whatsoever except the obvious physiological distinctions. Why, then, do people enjoy the stupid "Men are from Mars, women are from Venus"-type books, articles, TV shows, and stand-up comedy routines?
The first reason for this silliness is, of course, that it simplifies our understanding of the world around us. We divide the entire population of the planet into 2 huge groups, assign a list of characteristics to each of them, and immediately feel that the world has suddenly become so much more comprehensible. Who cares if these distinctions and the characteristics we assign to the genders have no basis in actual fact? Who cares if real people suffer their whole lives by trying to inscribe their complex personalities into the normative vision of gender? At least, we now feel so much more in control of the universe.
The second reason is, in my opinion, that this worldview gives people with miserable personal lives an explanation for their lack of personal happiness. Instead of looking at what they might be doing wrong in their emotional and sexual lives, they can put all the blame on gender differences. "Who can understand women?" they say. "Women are just too weird (emotional, incomprehensible, unreasonable, etc.)." Of course, women do the exact same thing.
Such people are particularly invested in promoting the discourse of gender difference. If this discourse gets debunked, they will have to deal with the unwelcome realization that their personal lives suck not because men and women are "essentially" different, but because they never took the trouble of learning how to confront their own personal issues and construct relationships with other people.
There might be other reasons for the almost religious belief in gender differences and I will definitely keep looking for them.