Fuel must be vaporized and mixed with air to ignite and the mixture has to be rich enough for the fuel molecules to be close enough together for an ignition chain reaction. This is more important in a gasoline engine because a rich enough mixture must be in the tiny area between the electrodes of the spark plug for ignition to start. In a Diesel engine, the ignition can start any place in the fuel mixture.

A Diesel uses less fuel at idle because a Diesel uses a stratified charge. This is where the fuel is richer in the small ignition area and then expands to effect an overall much leaner mixture.

In gasoline engines, the gasoline is mixed with the air before entering the combustion chamber and the total fuel mixture must be even richer in order to ignite at idle. That is why carbureators had a separate idling circuit.

The Honda CVCC engine was a stratified charge gasoline engine. It had 2 carbs one for the rich mixture and one for the leaner mixture. This was done mostly to decrease air polution because it used an overall leaner mixture.

I doubt that a Diesel uses 1/80 of the fuel of a gosoline engine at idle but is is a lot less for the above reasons.

P E H