Re: WTA Elo Ratings - revised (04/11/2013)
I can see at least three of problems in using an Elo rating system for tennis.
The first is the variable of the physical condition of the players. If a low rated player beats an injured or fatigued high rated player, their rating is greatly inflated. An extreme example of this would be Minella def S Williams 0-6 0-4 ret. Such a result would give Minella large but thoroughly undeserved boost to her rating. The same effect could happen to a lesser degree if a player is fatigued, either by having played a tough match late on the previous day or by having to play two matches on the same day.
Secondly, it ignores the factor of the importance of the match. For example, should Petra Kvitova's win over Sharapova in the Wimbledon final be rated the same as Razzano's win over the same opponent in the 1st round of the Fed Cup (an event Sharapova cares nothing about) earlier that year? Tennis is a tournament sport and the ability to win the big matches should be a significant factor in rating them.
Thirdly, the system doesn't change quickly enough for a sport where players can improve or decline quickly with age or form. Venus Williams, Stosur, Kanepi and Vinci's positions in your ratings are evidence of this.
The system works well for board games and video games but I'm unconvinced that it applies quite so well to sport.