I agree there should be an option to install. If R* already has written code for the game to run from the HDD on the PS3, I'm sure it could figure out how to do it from the HDD on the 360. Indeed, it will have to for the DLC. Maybe MSFT will move in that direction soon - R* execs have said that it had issues with the 360's storage solution(s) and that they had conversations with MSFT about that and MSFT understood. So maybe there is hope on the horizon.