Why are auto companies reluctant to offer “clean diesel” vehicles in the US?

I read this this morning and was absolutely appalled. http://www.businessweek.com/magazine/content/08_37/b4099060491065.htm?chan=autos_autos+–+lifestyle+subindex+page_top+stories Ford, an American auto company who has been taking an absolute beating from companies like Toyota and Honda in the fuel efficient vehicle market, has a nice looking 5 passenger car that gets 65 mpg. However, they are not planning to sell it in the [...]