You can't buy cards directly from AMD, they sell their cards to board partners like MSI, Gigabyte, ASUS and the like which are then sold to you. In the case of most of the 7990's, the board partners just slap their own sticker on it and sell it off. Though with other cards, often they will put on their own coolers and on some cards they will design their own PCB's to replace the reference (from AMD) design.