Easy, you do realise both ATI and NV are corporations right? They have no ethical code, and will follow the rules of business to the letter. That means they'll charge whatever they can get away with. You don't think AMD are charging very little for the Phenom because they're trying to be generous do you? Cast your mind back to the Athlon FX series.
Incidentally, you don't think a 4870 costs ~£180 to manufacture and distribute do you?
NV didn't suddenly 'realise' they were ripping people off. You don't think they had a meeting and went 'omg! Do you realise we're making too much money!?! We better give it back to our customers!'. No! They reduced the price far more rapidly than usual, and some OEMs (not NV) decided to refund people the difference to keep them sweet so they'll buy more cards in the future.
You're making the mistake of getting emotional in a non-emotional part of the world - business. They want your money, and they'll do anything to get it.