In tennis (as with many/most sports), there is unquestionably a HUGE difference in skill level between the males and females. It is not sexist to point that out. It is a fact (but should ALWAYS include the fact that there are clear genetic differences beyond the athlete's control involved to explain the reasoning behind the disparity). The difference in skill however does reasonably account for pay differential, because many people would rather pay or devote their time to see the best human competition, regardless of what sex the competitors are. The top ranked men are better able to deliver that level of competition and skill demonstration.

As a well known example, a few years back the William's sisters (then the best female tennis players on the planet at the time) rather arrogantly claimed they could easily beat any male tennis player who was ranked 200 or above, and then, when push came to shove and they had to play a guy who was ranked over 200 in the world rankings for an exhibition, they were utterly destroyed. Hell, the guy they played even took smoke breaks between sets to puff on a cigarette! Lindsay Davenport has also discussed how, when she was ranked #1, she would practice against her brother (not even a ranked male player), and he would routinely beat her easily. Pay disparity clearly has a lot to do with advertising draw and TV ratings. Like with the NBA versus the WNBA, there is clearly a very large skill differential.

Women's hockey is another example of a massive skill disparity. The gold medal winning Team Canada women's hockey team, during the run-up to the Olympic Games, practiced against men's high school (who are actually "boys") and men's college teams, and routinely got their butts handed to them as well. The women hockey players get paid virtually nothing, where NHLer men get very well compensated for their efforts, because they are more fun to watch because their skill and performance level is, due to genetic reasons, just higher.