ORIGINAL: TFF
The reason, it is possible to use less oil, is because the oil that makes it into the crankcase is not consumed. With 2 strokes, the oil in the fuel is only passing by bearings as it is going to be carried along to go out the exhaust. What oil makes it into the crank case in the 4 stroke stays in the crankcase to be used until it is ejected out the drain; it accumulates. With some using high amounts of nitro, the extra oil is a buffer from problems, but one of the original selling points of the first OS 4 stroke was it could use 10% oil for the haters of oily planes.
Less oil? 10%? All the fuel I use has at least 18% oil (as recommended by Saito). My understanding was that 4-stroke fuel has MORE oil than standard fuel for 2-strokes.