Why u people dont get both RB 2 & GH 4 ?? its better.
Unless something changes between now and change, their instruments probably won't be compatible with each other. Cept the Mics. And as some people have suggested, most possible buyers will only want one set of fake instruments in their living room.
DUDE, For the last time, THEY'RE NOT RIPPING OFF. Harmonix didn't even really "Make" Guitar Hero.
Yes they are ripping off Rock Band. Harmonix repackaging and selling an already established Japanese game with a third party peripheral maker (Red Octane) as their publisher for the orginal Guitar Hero doesn't change much other than it's possibly tradition amongst the sub-genre to keep one-upping each other with knock-offs.
I honestly don't care though. Whoever delivers the better Band game in the end wins my money. And if GH IV is the better game like you suggest (and I'm leaning that way myself) then so be it. I'm really not all that concerned about who did it first when it comes to entertainment, just who does it best.