Even though I know the answer to my own question, I keep Googling various keywords to try and find some glimmer of hope that Guitar Hero III fans using any supported platforms can play together.  I don’t know the specifics of the online play, but I’m suspecting that RedOctane is hosting all of them and developed the various incarnations of the game from the same core.  So can anyone tell me why this shouldn’t be possible?  Can the online play be hacked to be hosted elsewhere to support multi-platform online play?

Anybody out there?