Don't forget the testing standard is completely different between the 2 countries. After adjusting for Imperial gallon, the Honda Fit gets 43 mpg combined UK vs 31 mpg combined US. It's the exact same car, but tested differently.
So, if you combine all of these factors (Imperial gallon, testing standard, using smaller engines) you get a big discrepancy. Unless you live in the city, 1.0 liter is too small for 70 mph America. That's why it's not offered here.
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