The 480/470 were dogs for nVidia from a profit standpoint. They can't wait to drop these like a brick and move on to the 5xx series.
newegg prices (quick search for low price)
480 selling at ~499$ : 529mm^2
470 selling at ~259$ : 529mm^2
460 selling at ~170$ : 368mm^2
now if we look at "$ sales price" / mm^2 :
480: 499$/529mm^2 = 0,94 $/mm^2
470: 259$/529mm^2 = 0,48 $/mm^2
460: 171$/368mm^2 = 0,46 $/mm^2
As you can see, Nvidia probably currently have a easier time, makeing profits on their 470 and 480 than they do with their 460. Why would you want to drop the best profit makeing cards like a brick?
I know the 5xx hopefully have more performance/mm^2 so nvidia can start makeing profits again but still.... Even the 460 could use a refresh when compaired to the 6870.
6870: 239$ / 255mm^2 = 0,93 $/mm^2
Now each time nvidia sells a 480 for 499$ chances are good its makeing profit on that cards sales because of its price / die size. The 5xx Series will lower the prices the 480 can be sold for.... so will the 69xx cards.
I dont think nvidia are perticularly thrilled with the idea of haveing to sell the 470/480 for less.