What ATI model are you talking about?
ATI make a reference cooler for a card. After the cards have been out a while the individual manufactures start to adopt their own designs. Maybe of them are consistent with THAT particular brand of card. For example, all the Sapphire coolers from this gen and last gen may look similar or the same. It just takes them time to make or adapt their own designs to the new card. I think the only ATI refence cooler that has changed with the 5000 series is the 5770. They found the the cooler on the 5750 actually works better than the reference 5770 cooler. So they many companies adopted the 5750 reference cooler for the 5770. Other than that what you are seeing are non-ati coolers.