Rock Band is developed by a company called Harmonix, which developed Guitar Hero 1 & 2. Activision bought the company Red Octane which developed the Hardware for Guitar Hero, and MTV bought Harmonix. So they no longer work together and Harmonix did not develop Guitar Hero 3.
At this point, both sides are kinda pointing fingers at each other as to whose fault it is that the Les Paul PS3 controller doesn't work, but Harmonix has developed a patch that would fix it, but Activision is blocking the release of the patch. (
wiki info )
Full Disclosure: I'm a little quick to defend Harmonix as my college roommate is a developer there.