The politics of this announcement are interesting, as the next iteration of Guitar Hero will be developed by Neversoft instead of Harmonix. Harmonix, meanwhile, is working with MTV and Electronic arts on Rock Band. If Harmonix owns the rights to the Guitar Hero controller, it could mean Neversoft will have to develop a completely new one for Guitar Hero III. Throw in RedOctane's (and thus Activision's) legal battle with The Ant Commandos and it gets even more confusing.
Granted, GHIII is still a ways off, but we don't relish the idea of dishing out gargantuan sums of money every time a new music game hits.
Here's hoping the X-plorer will be compatible across the board.