I guarantee you that the ratings and revenue from two scrubs with the same talent as two hotties would be MUCH less, sports is as much marketing as theatre these days.
I've been watching tennis keenly for over 20 years and although I personally like a good competitive match and a showcase of skill no matter who's playing I also know human nature and can call a spade a spade. I also know that revenue drives salary and if the girls are bringing in their fair share of revenue - which they have been for some time - then they should be paid equal regardless of whether they work less for it. This is not a gender statement, just business.