Its not that the diesels can't meet emissions, its how they are tested for emissions.

G@ssers are certified by emissions per mile.
Diesels are certified by emissions per horsepower-hour.


Thats why the VW Touareg V10 TDI can look like one of the dirtiest vehicles on the market yet a V8 powered SUV that gets half the fuel economy can be certified as an ULEV.