As someone that doesn't have GD:RB, I don't mind this.
I will cite that they've just established, in my mind, pre-RB3 DLC as worth $1. With that said, this doesn't strike me as a heavy keyboard group anyway, are they?
Gonna listen and judge, as normal... but I honestly see no reason to not use this as an excuse to have more 4+ track weeks for a while. Three new DLC + 2-4 Green Day tracks a week would kick butt.
Heck... the more I think of this, the more I like this precedent. I think the Wii folk would love it if RB1 were released this way, as an example.