This puts the range of people who own a Wii and a HD console (or two) at roughly 25 Million, which demonstrates that there is a large base of users who would be interested in high quality conventional games for the Wii; and that it is probably a waste of time and money to "port" inferior versions of HD console games to the Wii months/years after they have been released for the HD consoles.
To but this into more solid numbers to demonstrate my point, if 25 Million people own a Wii and an HD console you can probably estimate the number of Wii owners that are at least somewhat interested in conventional games at more than 37.5 Million users; but this would mean that the number of Wii owners that are interested in a game like Call of Duty 4: Modern Warfare several years after its HD console release is roughly 12.5 Million.
