For your "average car", driving at 160 kph/100 mph requires 3x the energy as 110 kph/70 mph (due to aerodynamic drag), while only increasing velocity by 1.45x.

For your "average car", driving at 160 kph/100 mph requires 3x the energy as 110 kph/70 mph (due to aerodynamic drag), while only increasing velocity by 1.45x. Simply put, you're requiring 2x the energy per unit distance, which pretty neatly lines up with losing half the manufacturer rated range.