In an official post on the Rock Band forums, Harmonix Developer HMXSean revealed that due to the PLAYSTATION Store not having an update next week, the Rock Band DLC will come a week after schedule.
"Harmonix DeveloperHopefully, your presents will keep you occupied.
There will be DLC next week. An announcement will go out today or Monday.
Sony's offices are closed next week and the DLC will be postponed for a week until they come back (but they'll be back on schedule the following week when they get a double-dose of DLC awesomeness). It will go up in the Xbox Marketplace as regularly scheduled."
[Via Kotaku]