The US has had a harder time in forcing the oil industry into supplying the low-sulphur refined deisel fuel needed for the newer common rail diesel engines. Currently the sulphur content in US Diesel is 500ppm. In 2006 15ppm Diesel will be available. There was a good Scientific American article about it (unfortunately they charge $8 for a back issue .pdf) a few years ago. A somewhat informative link is here.

I believe that Europe already has the better fuel, hence the greater prevalence of diesel engines. ISTR reading that the newer, low soot diesels required the better fuel.

-Zeke