I've always received my codes either on a receipt or in the game case from Gamespot. Are you 100% sure about this?
With both Brink and Hunted, I've been told the codes would be emailed rather than on the receipt. That being said, I'm told some stores might still have them on the receipt.
If you're having issues with pre-order codes... make sure you post the following information:
The platform you're playing on (360, PS3, PC)
Where you purchased (Direct2Drive, Steam, Best Buy, Amazon, WalMart, GameStop).
This is because certain retailers will be emailing codes (like GameStop and Amazon) while others pack them in the box (Best Buy, Walmart)
Thanks
Update: I was also informed because of the situation with PSN, the pre-order PS3 codes might not be active just yet.