I'm not sure if the price premium people here are quoting are accurate, but it it is, the reason is simple. Supply and demand. Demand must be pretty high for the EcoDiesel allowing them to have premium pricing.
It seems that it now has been a year that diesel fuel prices are at or below regular unleaded. Saving is higher vs anything that requires mid-grade or premium fuel.
Add that to the fact that the E-Diesel gets significantly better MPG than the V8's (or EcoBoost), and it is easier to see why the average 1500 buyer would be interested.