Nope. It's not ram-bound, it's cpu-bound. Storing game state, when divorced from graphics, takes up a trivial amount of memory.
Here's the issue of Game Developer Magazine containing the relevant article. Here's Tony Cannon describing the three stumbling blocks of implementing rollback netcode:
Game state needs to be decoupled from audio/video state, there should be enough available CPU time to simulate several steps of game state per frame, and the simulation must be deterministic, based only on player input.
Memory is not an issue. SF4 could've used GGPO. Hell, KI could've been released on 360 and still used GGPO.