QFT, the beauty of it is that they don't have to buy the DLC if they don't like it. Funny how some people take it so personal when their favorite songs aren't announced.
I for one will be buying GH4 and keeping rockband. I love music that much that I'm willing to pay for and keep both games and purchase all the DLC that I like.
I don't know about GH4 yet, but I will be getting GH:A for sure. It really depends on the soundtrack, but I will continue to purchase DLC for any game that produces songs I like (or in the case of Rock Band, anything). In fact, within the last week I have purchased Muse on two seperate music titles. Life was good.