Since i live in Europe, I can say that cars over here seem to be smaller that american Cars, far less pickups, etc...
With my car now (basic Citroën berlingo van) I do an average of 6L/100KM. Pure coincidence that i also drive a Citroën, but i got mine from my work, and Citroën is one of the cheapest car brands you can get over here, you see?
As far as emissions go, we pay taxes accordingly, so cars nowaydays have very low emissions.
I think the main reason we have better MPG cars over here is smaller cars and smaller engines. A factory car with a V8 is almost impossible to get here (unless it's a sports car ofcoure), even a V6 is very rare. Most cars here have a L4 or even an L3.
Powerwise, most cars here are around the 100HP mark depending on the weight of the car.