Who said that artists steal? Whoever it was probably wasn't talking about Activision, who's pretty close to stealing Harmonix' idea for making a band game out of the Guitar Hero-styled play. Which is interesting, because it still is Guitar Hero. Hint hint.
Why? "Guitar Hero IV's not just about guitars," Activision CEO Bobby Kotick told IGN. "We'll include a lot of other instruments, vocals. It will help us expand internationally." Considering how well Guitar Hero 3 did in the US and not much else, it makes sense that the US's now #1 game publisher wants to expand it's ever-growing horizons across the pond towards Europe.
What does it mean? As of now, we know that vocals will be added, though whether it'll have Rock Band esque drums, the tuba, saxophone or flute is beyond our knowledge right now. Don't worry though: with Guitar Hero: Aerosmith and the portable Guitar Hero: On Tour set for release pretty soon, we'll be hearing plenty about #4 soon enough.