Ultimately RB2 vs GH4 will be about the song selection.
RB is doing at least one smart thing, carrying over DL content. If they have the ability, they should make all the songs from RB1 available as an inexpensive DL if you have an install of RB1 already, so that there is no need for disc changing.
But they have already pissed off Wii owners, now PS3 owners are going to have their turn at a meltdown. I wonder how long the exclusive is?
Wii Code 3456 7941 4060 2924