Didn't someone try and argue once that she was bigger than Michael Jordan becasue he asked his roomates who Michael Jordan was and they didn't know who he was?
I do tend to think that some of us get carried away with the value we place on our favorite tennis players.
Women's tennis was probably most popular in the late stages of the Evert-Navritalova rivalry, coinciding with the Graf/Seles era.
Of course the Serena, Venus, Henin, Hingis, Davenport, Sharapova stretch, was a great ratings era as well for the WTA.
Many times, the women actually out drew the men, both in attendance, interest and ratings. But that was all formed by great rivalries and tennis, not glamor (no matter how hard some of us want to believe that), and of course the men having poor, random, unexciting champions and rivalries.
For example, Kournikova wasn't good for ratings or attendance at a big event, though she was good for herself (the money she could make on her own outside the sport).
Now obviously Sharapova is a bigger winner than Ana, so I'm not directly comparing the two. But it is true, that the money you make for yourself is not directly related to your popularity within and outside your own sport.
It's just that in certain individual sports, if you fit a certain personality (good looking, girl/guy next door, etc.), and/or have a certain status (#1), you're going to make lots of money, regardless of your overall popularity.
Formula one drivers make bundles of money, and most people have no idea who they are or would watch their sport. Phil Michelson, the Golfer, makes between $40-$50 million dollars a year, and no one outside of Golf has any clue or cares who the guy is, even in America where he's from. Get the point? It's their sport and how they fit into the marketing niche. Michelson makes more money than Lebron James and Kobe Bryant in endorsements, but he's certainly not more popular than either one of them in America. Not by a long shot.