The original person who probably posted at those sites that MK

A is one penny at CC probably worked there and recieved the promotional copies of the games and saw that they were one penny in their system.
Except there's one catch, and the catch is they're only to be sold along with Psi - Ops since it's part of the promotional deal.
What does the promo copy look like? It's got a red rectangular box that says "promotional copy" on it, and if they employees at CC are smart, they wouldn't be placed on the sales floor for anyone to pick up, they'd be at the counter or placed next to Psi Ops for the person picking up the game.
At Gamestop, the promo disc goes under the description "premium, Mortal Kombat DA free w/ Psi Ops" (or something like that) and has no value, it's given out to people who reserved the game. I know because i (sadly) work there.
So to all those people going out there plucking regular copies of the game off the shelf and expecting it to be a penny, it's not. You just have to be lucky that an idiot empoyee left a promo copy out on the floor, you bring it up to the cashier, and the register biscuit doesn't bother to notice it's part of a deal.