Reading this thread it seems like fanboyism is alive and well.
Seriously though, if there are some key features in RB2 that won't be in GH WT, then RB2 may help sell systems as Christmas rolls around. But if they are pretty much the same then most will wait for GH WT on other platforms.
For me, I really like RB more then GH and not because of the instruments, the game feels more natural for some reason and I like the music selection more. But that is just an opinion.