RE: wal-mart guns
I don't know about how this works with respect to guns but it isn't a complete myth. I know that Home Depot does this with a lot of items that you find at a cheaper price than what you see at other stores. They negotiate special deals with the manufacturer. The products are built with cheaper components etc... I have two cousins that work at the Depot who have verfied this for me. Most of the changes are insignificant though.
Again I'm not saying they do this with guns.
Tom