I disagree. First, the human mind is not that good at dealing with decimal and numbers between 0 and 1. My car is rated 4.5l / 100 km, which is easier to deal with than 0.045l / km.

For a simple calculation, say 5km, what the easiest 0.045 * 5 or (4.5/10)/2 ?

Secondly, a car is designed to be driven over distance, so making measurement on only one kilometer wouldn't be representative of real world usage.