Unless you asked, I doubt they were sold out. All the walmarts in my area only hold like 4 units behind the glass since they are so big, but they have tons in back storage. (I've asked before)
The same goes for Wii, but it is more likely they have none. I've gone into a walmart before that had 1 unit in the window, and asked a clerk a few seconds after another lady did. Luckily they still had some in the back.