I wouldn't doubt the entire process went like this:
Carmack: "Hey Microsoft, can you guys waive the royalty fees for extra disks?"
Microsoft: "no"
Carmack: "How's about let us mark this game as HDD requried?"
Microsoft: "get out of my office"
Carmack goes to Sony
Sony: "What do you want?"
Carmack: "I'd like for you to fund and market this game in exchange for exclusivity"
Sony: "Ok....go on"
Carmack: "Thing is, Microsoft doesn't have a storage medium required to make this game as we envision, so unless you fund this project, we'll have to gimp every other version so we can make more money"
Sony: "This Rage game would be a technical showpiece for the PS3... and there's no reason to gimp a perfectly fine game... I'll accept! fill out this paper work and we have a deal"
Carmack: "Thank God, This is a dream come tr-..... wait, this contract says that we have to hand over the I.P to Sony corp."
Sony: "uh huh and?.... don't you know? we don't fund new franchises unless we get the I.P rights, you know, so you guys don't go multi-platform in the future and screw us over later"
Carmack: "well, we at Id games, usually keep the I.P for ourselves since we have such a rich history and important role in the industry...so I was thinking... how's about letting us keep the Intellectual proper-
Sony: "Get the fuck out of my office."
Carmack: >_<
Six months later in an interview....
Carmack: "I'd say the only thing that makes the PS3 better than the 360 is BluRay, but in terms of programing and graphics, the xbox360 is better in every way. With that being said, because Microsoft planned so poorly for the future, we actually have to gimp the PS3 and PC versions to accomodate the Xbox360. This is the reason why the 360 version will look worse than the PS3 version, but the PS3 as a machine still sucks."