I have noticed that Amazon have Guitar Hero up for preorder on the Nintendo Wii. The price of £32.99 seems quite good compared to the price on the PS2 and Xbox 360.
Amazon have a history of pricing this game wrong. I managed to get both Guitar Hero and Guitar Hero 2 on the PS2 cheap when they mis-priced it early on. They did the same with the soon-to-be-released GH2 on the 360.
Therefore, this screams mis-price to me and is probably worthwhile pre-ordering. It can always be cancelled later on!