According to the official Rock Band Store, the rumors seem to be true. Rock Band for the Wii has been pushed back to 2009. The good thing is you will only have to wait a few days for its release on January 5th. Normally I would say the 5th was a place holder date, it still may be, but this is coming from the official Rock Band site, so that makes me believe that it is the real release date.

Thanks J031 for the tip!