And let's face it: Rock Band version 1.0 to version today and Guitar Hero 1.1 to version today have all started out over the shark.
Guitar Hero was a neat, unique, niche idea, using a specialized controller do create a fun and enjoyable game; a simplistic parallel would be Duck Hunt for the original NES.
Only, instead of remaining a niche idea it had a popularity explosion, creating immense market pressure to provide even more content that is exactly the same yet also even better at the same time, which is basically impossible.
Sure, Rock Band was the logical extension, but there's a reason guitarists are idolized over other band members/positions, and there's not a whole lot more the concept allows for.
So Guitar Hero was getting ready to jump (and the absurdity made it fun), and Rock Band was midair (again, being even more over the top makes it fun), but everything after is accused of being the same gimmick with a new coat of paint - because it is.
Yet, they have to add something that is actually new in order to sell the latest (and only full price) version of the game, especially in the days of digitally downloaded (and pirated) content on consoles.
In other words, moneymoneymoneymoneymoneymoneymoneymoneymoneymoney.