Using your logic video cards prices would be $4000 by now since you equate % increase worth same % price jump.
Sorry most ppl won't buy there. Instead we will wait for moores law and pay same for double like we are used to.
I'm pointing out your faulty logic of saying amd is giving users a lousy deal because gtx 580 was $500 and for the same old price of $500, nvidia is giving you a nice performance jump, but amd is not at the same price point.
You're assuming the 6950 was fairly priced. It was underpriced in comparison to the old top dog (gtx 580) and now the 7900 series is fairly priced in comparison to the top dog (gtx 680).
The 6950 to the gtx 580 is similar to the 7950 to the gtx 680 in terms of fps competitiveness. So if the 6950 was selling for $380, you would wrongly say that amd users are giving a fair deal because for the same $380, users get a nice performance jump. But AMD was giving users an awesome deal in the 6900 series and is now giving users a fair deal.
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The top dog uber card has always been priced about $500. If they could charge $4000 and keep the same sales numbers they would. But they also need to keep in mind unit sales. The 7970 beat the gtx 580 and came in at 550. The top dog card sets the price and the rest of the stack falls in line. The gtx 680 could've been priced at 600, but there's a beautiful thing called competition.