It's not about how long they're on the court, it's about how many butts they put in the stands (read: revenue generation). The woman's game is just as popular (if not more so) than the men's game. I'm sure there are pleny of people who've never heard of Roger Federer. How many do you think have never heard of Maria Sharapova or better yet, Anna Kournakova (and she doesn't even play anymore!)
Expecting the same exact performace from the women as the men makes about as much sense as determining the prize money for auto racing based on how fast the cars are.
