Europe has stricter emission standards, I'm not sure where you get your information from, but if you check out dieselnet.com and do some research, you'll see that in California (possibly the greenest state in the US) has average C02 emissions of 323 and 429 grams per KM for 2009 as opposed to Europe's 171 and 157 grams per KM in 2003! So 7 years ago, Europe's emissions were still 2 to 3 times lower than those in California.
Hmm could be, just keep seeing that there are so much more emission items on cars like Eurea Injection and exhaust clean up that it has been cost prohibitive on most of the diesel to bring to the US. I just wish we had all the goodies from Europe! I can't find a decent high MPG car that can carry 5 people with ease and also there cargo. I have to look all the way back to a 1996 Passat Wagon TDI. 50 MPG. Based on the Audi chassis. Biggest wagon VW ever made! You can stuff 25 gal. in it! Some people can get over 1200 miles on one tank! LOL! Nothing here that can touch it yet and still pull a 1500lb trailer! Oh well some day my Diesel Mini Van will show up. At least I hope so.
This is the thing, the cars that do 60 to 100 MPG in Europe are usually very light and small with small turbo charged engines. However the biggest economical car i can think of was a Peugeot 307, seats 5 with a fairly big boot and it did 126 MPG by some people who broke a world record over 3700 miles! As soon as you want power etc you have to add weight. On saying this, the new Jaguar XF has a 3.0 litre diesel engine with almost 300 BHP, does 0-60 in 5.9 secs and still does 42 MPG average which is acceptable for a large vehicle. At least fuel in the US is cheap ours is still almost $7 a gallon and it's set to go up again!