Since right before D&D 3rd edition came out I have (on and off) been deriving formulas for the various tables and creating statistical spreadsheets to analyze the mechanics of combat and the game in general.
The purpose of it all,...I don't know. I guess just because these activities can give you some insight into why the designers created the mechanics the way that they did. Other times I can gather they didn't give the math too much thought. Ultimately its a hobby that might lead to writing an rpg myself.
I like coming across articles gamers write on the internet involving an analysis of the game. I don't think an actual book would be of much interest to gamers though.