There were quite a number of reasons that Harmonix released The Beatles: Rock Band as a new game rather than just a track pack, which mainly revolve around too many game engine changes to incorporate the songs into RB 2. They wanted the game to be a Beatles experience rather than just a few songs? Was this the right move? I'm disappointed because now I can't go out and add one or two Beatles songs to my RB2 game and I know I won't be buying this game because I'm really not much of a beatles fan. That being said, it's true that Harmonix didn't have to make these game engine changes but here's a question:
Who is going to be interested in a game that's clearly for Beatles fans? Beatles fans, right? How many Beatles fans are there in the world? *A lot*. I don't think Harmonix is too concerned about alienating fans, simple because of their choice of one of the most popular bands who ever existed.
As for some new features that were included which could not have been brought to the game if it were simply a track pack. because of the sheer complexity to add to Rock Band 2 and the effect it would have on the coding of other songs in the game (or even patch download size, which would at least mean it couldn't exist on Wii):
1) Multi-part vocal harmony support.
2) Custom venues (and no venues from Rock Band / 2)
3) New structure for Career mode
4) Different unlockables (Beatles memorbilia, rather than songs and options)
5) no character customization (you're a beatle

)
Harmonix was really going for an experience feel, which, while I completely agree sucks for non-Beatles fans who won't want to spend $50 or $60 on this game, seems to have quite a lot of appeal to the hundreds of thousands of Beatles fans who enjoy video games.
How many other music games have multi-part harmony? How many other music games let you be *The Beatles*?
Exactly.
Smart? Dumb? I can't say but the game at least seems profitable so far.