IMO, if Okami Wii sales beat PS2 sales(by a noticable margin) it would be a proof that even the niche, hard core orientated game have good chances on Wii. I hope that will draw all the smaller and innovative dev teams around Wii and that we would be able to play some fresh new IP's.
Those that are more dependable on graphics will always lean towards x360 and PS3.
As for the other part of the gaming population, Wii will absolutely outsell PS2 in the casual market and thanks to that it will pass PS2 lifetime sales. Thanks to WiiFit, wii could capture lots of people that aren't really interested in games, but are just amuzed by the fun way to excersize.

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