Entroper on 29 October 2007
I think they're having supply issues with the guitars; they can't make them quickly enough, so every one they have is being sold with a copy of the game. They'd rather get more copies of the game out, and it's not like Wii users have much use for a copy of the game that doesn't come with a guitar. GH3 is multiplatform and being released right at the beginning of the holiday season, so supply is really tight. There probably won't be a standalone guitar SKU until January or February.
