Also, the Price/Mile is the Great Equalizer in that it doesn't matter if the car uses Gasoline, Diesel or whatever fuel...it always tells the user how much money it takes to drive one mile.
We may use different fuels but money is common ingredient we all share. For example, I have both diesel and gas cars. The Price/Mile lets me know which ones are the least expensive to drive...I don't care if it's diesel or gas, I know how much it'll cost per mile to drive it. Lower numbers are better.