They get poor MPG because "america doesn't want slow cars".
The smart here in Canada used the diesel and got awesome MPG. (0.8 litre diesel, 40 HP, can go up to 130 KMH). 51/60 is the US MPG rating if I convert its liter/100 KM.
The one we have now has the more powerfull gasoline engine. Quite the downgrade...
Now please stop bashing the car, it's the same reason we have 105 HP Honda fits and no option of the sub 100 HP engines all europe and Japan has. (And a whole lot of other cars). America always gets the **** end of the stick in both economy and powerful engine of the spectrum when it comes to imported cars.
I drove one of those diesel one and for town use, it's all you need. It reminds me of a scooter, you can drive the thing floored and you wouldn't hurt anyone.
http://www.canadiandriver.com/articles/mc/06fortwo.htm
I really loved the thing actually, the inside didn't feel small (unless you looked at the back), and the stereo was descent(ahah), it didn't even feel cheap, just different, and everybody looks at you like you're driving a porsche (but not for the same reasons I suppose, lol).