The solo reason why price have not drop is due to supply. Due to the problem of TMSC, video cards don't hit the market with the quantity that was expected. It start last sept., where 5870 was out, but people can't get it. There was a lot of back orders and the card simply not on stores. It was until Jan, 2010 when we finally see some 5870 around. The same thing happened to Fermi, as 480 are still very rare. As of now, there are still people who wanted to upgrade their video cards, either wait for Fermi to hit the stores, or Evergreen to drop in price. Because of these demands, price stays.
Unfortunately, 480 is not as attractive as it should be, allowing 5870 to have a reason for its price, and since Nvidia won't release a faster card anytime soon, there won't be a price change for those cards. However, you may expect a small price change on 5850 and below, as Fermi is about to release Fermi 2 for the mainstream market at June[Rumor 460]. It isn't going to be big, about 30 bucks give or take next month.
If things on the Nvidia side goes well, there may be a 485 sooner than expected. That will cut the price on both 480 and 5870 by a degree. That is my guess.