I'm afraid you are over-optimistic about the marketing industry you picked as an example of a woman-friendly sector as far as hiring and wages are concerned. In some countries it might be the case, but there are injustices there as well, as this article indicates: http://prosar.com/2015/09/17/its-time-to-close-the...
The 80% rule sounds like a very weak barrier. 80-20 is still very unbalanced, and it does not necessarily solve the pay gap. I feel that there's a deeper, systemic issue at stake here.