Later, I asked for clarification.

Two Activision representatives confirmed that the age of cross-game instrument incompatibility is nearing its end.

They explained that the Xbox 360 version of "Guitar Hero: World Tour" will indeed be compatible with the instruments for the first "Rock Band." The "GH" developers have, for obvious reasons, not been able to test their new game with the upcoming "Rock Band 2." Other third-party guitar and drum controllers are expected to work with "GH: World Tour" as well.

Activision isn't ready to address whether the instrument compatibility applies to Wii, PS2 and PS3 versions of "Guitar Hero" and "Rock Band." But a rep told me that a recent auto-downloaded title update to the Xbox 360 version of "Guitar Hero: Aerosmith" should make that game compatible with non-"GH" guitars, including the "Rock Band" ones.

This is what people were demanding, no?