It also has to do with our fuel. Diesel in the U.S. still has a very high sulphur content relative to what is available in Europe. This high sulphur restricts the ability to deploy the latest exhaust scrubbing technologies - the sulphur poisons the devices, much like leaded fuel was a no-no when catalytic converters were introduced for cars. The sulphur content of fuel in the U.S is scheduled to be reduced, but not for another 6 (??) years or so.

The rant regarding anti-diesel eco-nazis in the US is also true. For reasons that I fail to grasp, the US seems to consider the particulate content of diesel exhaust much more of a health risk than does Europe. Not sure who's right. As well Europe has some concern about carbon dioxide output - which is much lower for diesels than for equivalent gasoline vehicles. The US doesn't seem to care about CO2 output in the least.