Eh, they'll probably get them sometome soon.
I just want to repeat from my experiences with it, the game isn't really that hard by any means. Not as impossible as some shit is in GH. But in reality, it's probably better that way. I've been sort of arguing with some of my friends about which game will be better (yes I know, total nerd wank, but whatever), and I'm pretty certain by this point Rock Band is clearly going to be. The whole draw to the game is performing AS A BAND, and when you ARE playing in this mode, you aren't jsut responsible for your instrument, but for your whole band. If someone fails pretty miserably during a song, you have to "save" them using your star power equivalent. Being able to pass a song in Rock Band is going to be tons harder than in GH, as you have to be on the look out for every single aspect of the song, bot JUST the guitar.
I just wanted to say that to clear up some misconceptions of Rock Band's difficulty. It's no fucking Through the Fire and Flames, but it's going to be just as, if not more, difficult.