That is only part of Amazon's advertising business. If you read their 10-k:

"Vendor Agreements We have agreements with our vendors to receive funds for advertising services, cooperative marketing efforts, promotions, and volume rebates. We generally consider amounts received from vendors to be a reduction of the prices we pay for their goods, including property and equipment, or services, and therefore record those amounts as a reduction of the cost of inventory, cost of services, or cost of property and equipment"

http://phx.corporate-ir.net/phoenix.zhtml?c=97664&p=irol-sec...