Tell that to all the ebayers. They're going for $170-$190 USED (without shipping) on ebay. Plus, the cheapest I've seen (at newegg) is $250 after rebate.
I agree, the 7900GS beats it. But, the 7900GS is PCI-E, and the 7800GS is AGP, and one of the fastest (if not the fastest) AGP card...