No, I have a PS2 and 360, and I was thinking of getting Rock Band for the 360, except it doesn't entirely belong to me. My buddy's having me hold it while he's in Iraq, and I don't know when I'm getting my own. Since the PS2 is in every way mine, it's a possibility. Also, the PS2 version looks good especially if there is only a single guitar, since my buddy has a PS2 guitar, meaning less extra spending.
Personally, the idea of only packaging a single guitar in the box retards the whole idea of the game. Why couldn't they just put in another guitar? I don't mind paying the extra for another guitar controller, but it doesn't make any sense to me to force you to buy another separately. They can't possibly make that much extra profit from selling it separate, and people would more likely prefer an extra controller that they don't use over needing a controller that they don't have.