ATI 4800 series gets off the ground, snags top retail sales spot in September
 

AMD’s latest graphics chip series looked good on paper and good in benchmarks and it appears that it is returning good sales numbers as well. Nvidia is still dominating the list of the ten best selling graphics cards in U.S. retail, but 4850 and 4870 cards had a particularly strong showing, especially if we consider that the best selling graphics cards have much lower price points than these models.

http://www.tgdaily.com/content/view/39938/118/

The prices of them are just so low, that they still have an excellent FPS/$ ratio. So no reason to buy something slower.