Product performance is not the only measure of what it should cost. Quality, feature set, materials, design, and unit cost should all go into deciding the price a unit should fetch.
Sure. Which quality, feature set, materials, and design do you have in mind where the 7970 was trumping the GTX680 at launch?
unit cost: You want to reward AMD for being worse at efficient design? Do you believe that customers should have been charged more for the larger Tahiti die because it had disabled DP units? If Nvidia makes a very efficient die with a huge ring of empty silicon around it just to dial up the die area, would that satisfy your grievances?
A plastic spoon, a steel spoon, and a silver spoon of the same volume will all feed you at the same rate (performance). Are you stating that they should all be able to harvest the same price? Absurd!
Beautiful analogy: we have both plastic and steel spoons at work. People on start taking the plastic spoons after the steel spoon are gone. They just don't feel as well in your mouth. Silver spoons look way better at a festive dinner table. Another important KPI for some occasions. And, some people simply like to buy something more expensive just because they can.
What kind of KPI do think are important for a gaming GPU? Performance. Energy efficiency. Fan noise. Anything else? All things where a GTX680 excelled over the AMD flagship. Nvidia magnanimously priced it lower. Yet that still not good enough.