Well, if it is a test for RE5 it is a bad one because Okami buyers don't seem like very likely purchasers of RE5.
However, Okami will sell more on Wii than on PS2 for several reasons:
The lack of decent adventure/rpg/hard core games on Wii.
There has been much more hype this time around, more people know what Okami is now.
There is a lot of hype around all Wii releases.
RE5 would also sell well on Wii, but that has nothing to do with Okami.
I would cite regulation, but I know you will simply ignore it.