If they flood the market with the wiis, their product will go down in demand and value.
Sadly its true. A lot of people have shown interest in the wii because its hard to obtain. People want whats hard to obtain and the fewer there are gives the illusion of a greater demand.
Its merely marketing tactics by nintendo to keep interst in there system untill they can get more of their 3rd party games on the market as well as some other titles.
btw it doesnt help that there are people who have no job and just go around buying up all the wiis they can so they can resell them on ebay for way more than the recommended retail price.