Well the 7970 does have 384 bit, but that does not justify a $150 jump. Neither does the die size or yields, if according to AMD, they have good yields, or so they said to their investors. The price cannot be justified in any form other than "we asked this much because we could". Well now, they can't and should lower the price.
I was talking in general anyway. 4870>5870>6970 were very similar and the price increased by $50-100. 6870 to 7870 are very similar and price increased by $100. 2 Gb GDDR5 does not cost much more than 1 Gb GDDR5, as in 2x as much, it does not cost double, not eveb close, and it does not cost more than 1 Gb GDDR5 several months/years ago. 8 chips vs 12 chips does increase price more but not by $50 or anything close to that.
So their prices can't be justified now, neither really is GTX680's price, except for the fact that it's the fastest card and is actually priced lower than the competing card, so it's more justified.