A great selling point for many vendors selling GeForce cards is to have them come out of the box stock-overclocked, giving them a slight performance boost over competing cards with the same GPUs. Now, the ability to sell like that may also be given to ATI resellers.

ATI will provide a warranty for such chips and there will be some kind of validation process where ATI will be able to control the overclocking frequency. After you sell your chips you kind of have to give the warranty for them.
Some vendors have made themselves quite known for this practice, such as eVGA, and it's likely that this may encourage some nVidia-only vendors to try out ATI cards as well. ATI is no doubt looking for ways to better compete with nVidia this year following the continuing success the entire 6x and 7x series for them have been.