It appears as though the Playstation is getting a DLC that the xbox folks aren't, just like the Halo theme download that Xbox 360 customers got and Playstation owners didn't. The Guitar Hero Community site has stated that "The End Begins (to Rock)" from God of War II, will be available for download starting June 5th.
What the site doesn't tell us is whether or not the DLC will be Playstation only, or Xbox as well. As of right now, we can only assume that this killer track will only be available for PS.