In an unsurprising move (and already a precedent set by Final Fantasy XI, but ignored since), Microsoft confirmed at its Gamefest 2007 that studios working on server-based titles for Xbox 360 are allowed to require the hard drive for their games to run. Games allowed to participate in server-based's "bent rules" is decided on a case-by-case basis.
Microsoft will be asking developers to come up with a set amount of hard drive space to set aside for each game. For example, if World of Warcraft came to Xbox 360, Blizzard would have to tell Microsoft "the game's going to need 4GB of space," even if the game won't necessary install 4GB of content at the start.
