They need to profit from their cards in the time they can, and that is as much possible before nVidia releases counter parts. Its normal to shoot for the highest possible margins.
Also $150 is GREAT price. You get a totally capable card with newest arch, DX 11 capabilities, super low power consumption (I guess 20W idle and about 100 on load).
Considering LOT of people have not so great computers or especially Power supplies <= 400 W it will be awesome upgrade.
Notice that the new cards are 168mm2 die size which makes it LOT less than 4870/90 series so ATI is to really profit right now from them.
nVidia on the other hand can do only 1 thing. Lose.
They have a choice though - to loose money, or to loose market share. That will define if they will drop the prices and we will see price war (which ATI will win) or stay at current level and let ATI profit and take market share.
I hope for the price war