Why are the American imports generally less powerful than their European counterparts.

[Jax Humanhater]

Here is an example of a BMW from Europe and North America:

http://en.wikipedia.org/wiki/Bmw_m3#North_American_models

 

[Hiroshi Awazu]

Emissions regulations. It is more strict in NA.

 

[Hampus Andersson]

Not just that. I talked to a BMW worker and he said for the US market there´s even different electronics in the car. (not all cars i presume but definitely one model we spoke about)
Because of US laws.