Reader billdcon spied Resistance 3 and Gears of War 3 hot-bunking a PS3 kiosk at his local Walmart. "Not pictured, people asking for Gears for PS3, and Walmart employees actually looking all around to try to find a copy," says billdcon. We'll believe him.
A person who works for Wal-mart or in an electronics department doesn't necessarily know the ins and outs of video games. It's up to these companies to educate their employees on things like this in the simplest way possible. There should be a simple reference system in place that'll allow employees to look up a game or movie in order to see which formats it is or isn't available in, as well as which of the available formats is in stock.
Bear in mind that the customers (or whoever's requesting the products that they're buying) are partially to blame, as well. I used to work in an electronics department, and I lost track of how many parents treated me like complete shit because they wanted Mario on PlayStation 2 or Xbox at the time, and I had to be the one to claim to them that such a thing didn't exist. (I say "claim" because they still didn't believe me.)