Earlier quoted context omitted.
More U.K. “fun” examples: • Beer served in pints by on-licenses, millilitres by off-licences • Even though distances are all in miles, and petrol/diesel sold in litres, fuel efficiency is in either g/km or miles-per-gallon
The metric fuel efficiency measure is litres per 100km. This way round makes more sense -- "how much will it cost to travel X km" is a more common question than "how far can I travel with Y litres or £Z".
In essence I'd argue that most of the use of the any fuel efficiency metric is to simply rank cars, rather than to ever back out a genuinely useful cost/distance number. At which point furlongs per quart would be as effective as anything else...