@BKK2: Another small but possible interesting piece of information is a remark in this article by Matt about The Conduit:
"Just ask Activision, which gambled that Guitar Hero 3 for Wii would be a success, despite the fact that the genre was yet-unproven on Nintendo's console. Two million in sales later, the music title has sold better on Wii than it has for PlayStation 3 or Xbox 360."
So Guitar Hero 3 (Wii) LTD reached 2M and is now bigger than Guitar Hero 3 (360) LTD