[Anonymous]

MMORPGs are different because you need to maintain a gigantic database that stores each individual character's stats, location, items, and item locations. Then that database needs to have the ability to be constantly referenced and appended through normal gameplay, as well as when players and the game world change, all from loads of dedicated servers that simultaneously report the location, stats, etc. of every other player you see in the game world.

Nothing can be stored locally because then you could edit it. And cheat.

Battle.net isn't nearly as complicated because, while they do have a database, it's only referenced once upon entering the chat room and again upon starting a game or having another player join, with mostly direct communication between machines throughout to tell who has got what item, with information getting refreshed after lengthy periods from the official servers*. Not only that, but you can only have a handful of players in a battle.net, which, again, are all mostly managed among themselves in a game. And for things like Starcraft and Warcraft, the database isn't nearly as complicated since you start fresh every game.

* Let me know if I'm talking out my ass, but it's been done before like this and is the only smart way to pull it off.