According to Yahoo there are currently 3,600 EB Game and Gamestop stores in the U.S. (source: http://rss.news.yahoo.com/rss/videogames). Reading people's post, it appears that each store is averaging about 15 preorders (some may do more, some may do less). So if we take the number of stores (3,600) and times it by the number of preorders (15) that equals only 54,000 units have been accounted for."
I would think that Toys R Us and Walmart are going to get a huge bulk of the rest of the Wii's on launch day. You may be able to walk in without camping out to get one. There will be 1 million Wii's on launch day in North America, so 1 million minus 54,000 is.......946,000. Thats still a lot on day one.