It's only the same amount of fuel savings if you burn the same amount of fuel, right? The amount of fuel saved between 10mpg -> 12mpg may be roughly equal to an improvement of 30mpg -> 60mpg, but being able to go e.g. 600 miles (one 10-gal tank) vs 300 miles could be the difference between buying one tank or two (or: 1000 or 2000 over your car's lifetime).

Wouldn't that mean 30mpg -> 60mpg is more likely to save fuel on average because people are need less fuel to get them where they're going?

Or did I just get bamboozled by the trick?