The bottom line is that everything is supply and demand, and based on merit. One can ask for anything he wants, and the boss can likewise refuse to pay anything he wants. When the boss feels he is getting his money’s worth, and the employee feels he is willing to work for that amount, then that is one’s salary.
Apparently bosses feel that men are better at certain things than women. They don’t view it as the same work. Certainly, women are better at certain things than men. I am sure there are professions in which women are paid more than men.