Instead of trying so hard to prevent piracy by locking users out, just give the pirates a really good reason not to bother.
To be fair, the game is a great deal of fun now. If they launched the game 8 months later, it would have lasted a much longer time.
With all the new ISP bandwidth limits we're starting to see, I think a 25gig download would surely deter some people.
Guitar Hero 3 had a Foo Fighters track pack months ago, and now they feature songs (actually, the same song) in both new games.
You may still see some AC/DC in both games, you probably just won't see the same tracks.