(I work at Wal-Mart.) The reason why Wal-Mart gets their 'new-release' games after EB is because of the way they distribute their games. If Wal-Mart wants to buy 100,000 of a game, the distributor (such as Nintendo) will send the game to Wal-Mart's main distribution center (which I would assume would be in Bentonville, Arkansas). From there, the product gets split up, along with many other products, to go to the regional warehouses (on a truck). At the regional warehouses, the product gets split up by store once again and gets put on another truck to go to the actual stores. EB, on the other hand, has the games sent directly from the distributor (like Nintendo) straight to each and every store. It costs EB a lot more money to have to pay for the direct shipping, but customers get the games on time.
And it's very annoying that Nintendo doesn't cut prices on older games. We have about 12 copies of Mickey Mouse and 2 copies of NBA Courtside 2002 that will never ever sell at $49.96. If Wal-Mart marks it down, that comes out of Wal-Mart's (admitidly very large) pockets, but I think it may also come out of my annual bonus check (I'm not really certain of this, though). Anyway, it's not cool.

And I think it's shady that Microsoft doesn't have a set number of games sold or shipped. Rather they're games that are "proven to be all-time favorites". Ah well.