in my opinion, all this talk of a pay gap obscures the real issue of women in the workplace, which is a negotiation gap.
without giving too much away, I'm quite well compensated by a very large company, especially for my age and education level. but when I first got out of school I accepted a job offer paying much less than I was worth, even as a relatively inexperienced professional. and I'm not the only woman I know who put herself in that boat... women are socialized to be agreeable with authority, to "go with the flow" and take what they can get when it comes to career.
men, on the other hand, are more likely to ask for what they're worth. this is lost on many women who are happy just to have gotten the job interview. it took me a year and a few lucky breaks to realize that I could-- and should-- be earning more than I was and a few more years in top of that to get myself to the salary level that would give mr. spaceboobs and I the kind of flexibility we wanted (he's spoiled.)
so there is a gendered difference in pay, especially in highly paid positions, but it's not an issue of sexism so much as socialization. ladies, never take the first offer.