GameSetWatch has an interesting column up on the evolving nature of WoW; the rules of contest are frequently "in play", so to speak, in most sports or games, so why would a MMORPG be any different? Patches and additions codify, so to speak, some of the player-created games, but there are plenty of unsanctioned game making that goes on:
In fact, most people play a combination of four or five games in World of Warcraft. There's the leveling up game, which almost everyone plays ....
After this game, some people play the endgame game, in which they try to fill out their character with the best items, or the other endgame game, in which they try to beat all the raid bosses. Some people play the Honour System game, where they try to amass honour points, and others play the Arena game, where they get to the top rank in any given season. Then, there are the less popular games - or the one I just made up: going from one capital city to another as quickly as possible at level one.
Half Blizzard driven, half player driven - so Warcraft turns. It's a nice little look at games-within-games and how these things take on a life of their own.