There's an intersting new article at the game devoloper site Gamasutra. It deals with the lessons that World of Warcraft teaches. It's very insightful and interesting. The rules that are built into game designs (or slapped on top via "Terms of Service") say a lot about what the developers value and what players learn from the game itself.

Granted, there probably should be rules, to ensure that the majority of players feel like they have a fair and fun play experience, but a lot of those rules, it seems, could be coded into the game.

http://www.gamasutra.com/features/20060222/sirlin_01.shtml