Retailers scan game hardware serial numbers into their databases when making a sale; the receipt may even list the ever-so-unique number. But you shouldn't need to list the serial number on eBay to make a sale, so why do it? The EB/Gamestop bosses could buy specific listings and hope to catch employees, but that seems like a lot of costly work. Even then, the odds will be in favor of the EB/Gamestop worker-turned-profiteer.
People will make money reselling scarce launch hardware; that's a fact of gaming. We like the idea of EB/Gamestop trying to get consoles into the hands of gamers, but this plan may have little impact.
See also: eBay's PS3/Wii auction cancellations are a good move