Tbh the gtx780 is not much bigger than the gtx480/580. It also has 3 smx units disabled comparing to the full part so theres redundancy built in. The gtx580 was the full part and they got it to market at normal pricing. The process should have matured a lot over the amount of time they have had to work with it. With all this in mind I am pretty sure they could have done better with the price.
It's not bigger but has a massive amount more transistors. They also only Fab a single chip and Yields determine what it will become.
I agree the price could be better but I also feel it's not quite as bad as it could have been.
Look at the costing of the GK-110 lineup on OCUK all using the same K20 silicon.
K20 - £3000
Titan - £799
780 GTX -£569
They do not offer the greatest value when compared to the competition but compared to the others in it's family the 780 is superb value. I think comparing something that is hugely more expensive to produce and manufacture is not really a fare comparison in my opinion.
If you are worried about value then you would buy a 7950 or two. But there is a market for people who have no interest in value and want the exotic hardware that is a bit special compared to the rest, This will cost hence why the 780 is around £200 more than the 7970. Performance is not always the key factor in pricing.