I get what you mean, really I do, but I think this is something the majority of people will be fine with. We get to reach a bigger audience, the community has more people to Score War with or team up with on Goals, Facebook has built in tools to help and everyone gets a richer experience. Blitz is, of course, still more than playable without RB World and we had playtesters, PAX East and E3 attendees, press and early code folks going bonkers over the game months before we even announced RB World.
RB World is meant to be a companion piece, an additional layer if you want it. If you don't want it then you can still play all the songs, post high scores, get all the coins, get all the cred and unlock all the achievements without it. It's very much like the forums in a lot of ways, providing that additional layer to the RB experience for the people interested in getting more out of it.