I never played Okami on PS2 as I sold it just a year before, it's certain that I'll get it for my Wii. Don't worry, I'm sure this game will at least reach 400k surpassing PS2 version and making Capcom pretty happy.
And for the record, Zack & Wiki sold pretty well for such a niche title ( and is still selling ). I can bet some serious money that if it was released on PS3 / Xbox360 or even PS2 it wouldn't have reached even 200k.
My themeforest portfolio:







