You can basically sum it all up by saying that Harmonix employs actual musicians who are also very talented. Hence Rock Band being more musically accurate.
On the other hand, Neversoft are a games company who know a thing or two about making a good game. Which possibly explains why Harmonix rigidly stick to their principle of making you play songs over and over and over and over again during the tour mode - yes, we know real bands don't just play songs once and never again but it gets boring quickly.
This is one thing I will always stick to - all songs should be unlocked and accessible at any difficulty for Quickplay with no save disabling cheat codes from the moment you first start the game.