GTX 780 launched at $649, and it wasn't even the fastest single GPU when it launched. It was only about 16% faster than the GTX 680, and it was 8% slower than the Titan which was already out.
There are already GTX 1080 third party cards listed for $620 US. The GTX 1080 is the fastest single GPU available right now. It is over 35% faster than the GTX 980. It is over 20% faster than Titan X and 980 Ti.
If they don't sell as well, nvidia will drop the prices.
I agree that the entire concept of charging more for a reference card is ludicrous, but as already pointed out in this thread, this is about supply and demand.