And whole ranges of employees make less than other ranges of employees. There are lots of women in business that make 20 and 100 times what I make, for example.
Equal pay for men and women does not necessarily translate to equality at the workplace (it's based on a non verified premise that men and women's output and negotiating skills are equal). Have you researched if those women that make 10% less than men:
1) put 10% less to their work (e.g because they prefer investing more in their children than in the whole career rat-race)
2) Are less cut-throat salary negotiators? As an employee myself, I know that employees get what they are able to negotiate, not what they deserve and surely not equal pay.
Equality is equal pay for equal work -- regardless of gender race or creed.