I'm not surprised really. Look at it this way, there are OEM partners out there that make Nvidia and ATI cards. So when ATI comes out with a cheaper card that outperforms the competitors top single GPU for alot less money, they get stuck with alot of older cards. So if the prices rise, they start selling more of the older cards again since the new card isn't so attractive at a higher price. The other option would be to lower the prices on the older cards to compensate, but then they lose alot more money instead of gaining.
Look at the 4890 for example. Most are going for 180-200$, but you could get a 5850 for 50-60$ more that gives you DX11, more performance, eyefinity, and a bunch more. So now the 4890's get stuck on the shelf while the 5850's are flying out the door. The options now are to drop the 4890 to 150-160$, which probally cost 180$ to manufacture, resulting in a loss. Or raise the 5850 up to the 300$ price point, enabling more money to be made from the 5850, and then being able to keep the 4890 at it's current pricing of 180-200$.
If you look at Nvidia's situation it's even worse, so any OEM making ATI, and Nvidia cards(Gigabyte,XFX..etc) would be shooting themselves in the foot by selling a GPU for 260.00$ that outperforms a 350.00$ card with older technology.
I think this shortage was created so that older cards stock would be depleted more before bringing out the new cards in bulk. Thus allowing to market skim more by raiseing the prices on the best and selling the last gen to the people that cant afford the new tech. It's all business, and what they do is try to make money and cut losses when they can, which is exactly what is happening now in my opinion.
PS: With chrismas just around the corner, this will always happen as well. Just look at what hype did for the Xbox 360, and the Wii. Fake a shortage, and more people will want it more. Charge top price before christmas, and drop it back a week or two after claiming that there is no longer a shortage thus now allowing for cheaper prices, and a higher volume of sales because of the demand at that time. If you look at a few different websites around you may of noticed that not only are the 5000 series cards increasing, but the 4890's are now rising as well. I've seen quite a few 5770's that are now 210-220$, just above the 4890's price, or right on it. So now the 4890's are starting to sell out since they are faster than the 5770 at the same price.