Wow? Wow.
And I wonder how much of that success is because the game is now on multiple platforms to boot? Guitar Hero II is on the PS2 and 360; Guitar Hero III is available for Xbox 360, PlayStation 2, PlayStation 3, Wii, PC and (believe it not) Mac. GHIII also boasts an impressive 5 million downloads for songs to boot!
With those kinds of numbers, going exclusively for one system is looking more and more like, well, insanity. And I'm quite all right with that. The success of multi-platform games takes away the potential for excessive and abusive amounts of control on the part of console makers because publishers have multiple options ("You're not the only platform in town, you know."), and puts the focus back on game, not platform.
I'm happy ;)