If your example of gas vs diesel cost was true in every area and the only thing people wanted in trucks was the lowest operating cost for a limited term of ownership, you might have a point. Brand bias plays a big role in these decisions and some folks like diesels because of their excellent driving characteristics. Also the length one intends to keep something plays a role. It's funny too, that people have been wanting a more economical diesel truck for a long time. One that has less towing capacity is fine for those folks because they just want a lighter duty truck that is more economical than a one ton. Now that lightness is being used against Ram as being less capable so it's not as good. Sheesh.
I don't see the Ecodiesel as a tough sell at all, except to a Ford loyalist. People have been asking for smaller diesels for years and the Eco-diesel seems like a very good engine. I like diesels and will avoid gas if I can. The Ford eco-boost is using very modern technology with it's direct injection and turbo on a gas engine. Good for them, but they have a long record of very poor designs that end up costing consumers a fortune because they don't hold up.
I recently bought a new Cummins because I think they are the best engines available in a pickup and they are towing monsters. It's more truck than I need most of the time and I'm perfectly happy to accept that it will cost more to operate than an Eco-boost.