Update 8/27 - The natives were quite restless on the forums today, as Harmonix kept the Rush DLC delay explanation in a shroud of secrecy until pretty late in the day. It was eventually revealed that the album download is to be delayed 1-2 weeks. Not sure what went wrong there, but it had to be something significant. Most speculation is that it has to do with the YYZ song having no vocals. Probably, and something to do with how that worked in the live environment, something QA wasn't able to catch in their test environment (like remotely joining a group, or something like that), because it's not as if the lack of vocals somehow escaped their notice until the last minute. So I wouldn't be surprised if the portion of YYZ that is tambourine-friendly becomes a vocals part, if the theory that vocals are not a removable part holds.
Update 8/28 - Harmonix has offered some good news to balance this out though. The Hollywood Insider has the exclusive on the upcoming crop of full album DLC releases, and it's pretty impressive! It starts with Metallica's new record, Death Magnetic on Guitar Hero (this was expected) on September 12. But then:
Stocking the digital bins, EW.com has learned exclusively, will be seminal full albums by Foo Fighters (The Colour and the Shape), Red Hot Chili Peppers (Blood Sugar Sex Magik), Jane's Addiction (Nothing's Shocking), Megadeth (Peace Sells... But Who's Buying) and Stevie Ray Vaughn (Texas Flood), along with a specially-compiled No Doubt Best Of collection. All are slated to roll out in the coming months, according to MTV Games.
Stevie Ray. NICE! No Doubt. NICE! Jane's Addiction...awwww, doesn't include Caught Stealing. Alas. But some pretty exciting stuff coming down the pike.
You can also check out Rock Band 2's opening sequence.