Its Nintendo's own fault. Any "pack-in" game is instantly not counted, as the title "itself" never sits on the shelf, never is individually bought, etc.
But don't stress - it really doesn't matter. The strong Wii sales are enough to keep Nintendo happy, and this is in no small part due to Wii Sports.
Im sure if they had their way over again, it may have retailed for $250 - with Wii Play, not Wii Sports. Wii Sports would have sold for a budget price title along side it ($39).
Just look at the sales in Japan, and get a warm and happy feeling :) When is the last time a launch title (no - make that TWO launch titles) hit a million units within 10 weeks of sale?
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As for the 360.. I have a bad feeling that your pain is just about to begin :P MS are going to have to pull something out of the bag to restore the momentum that has been lost...