I used to think that way, till Nvidia released the 8800GT. Since then, we've always had the current mainstream card match up, if not outpace, the previous gen leader in performance. The 570 can easily go toe to toe with the 480. Amd just abandoned that approach and releases two of their fastest single cards on a die nowadays, as their fastest card. Something for which they get a lot of flak, but which makes sense, business wise.
Today, you can buy an 8800 Ultra for a tenth of the original price, just 3 years later.. I think the mid range and lower upper range cards are the better option always.