With the exception of a YS, the typical fourstroke crankcase would be getting nothing but hot oil and gasses that blew past the compression ring. Of course, the intake tube would be very cold and have moisture condensing on it. I always have to flush my Enya crankcases with oil after a outing because the blowby crud is so corrosive and will attack lower end parts quickly. I learned this lesson the hard way after being dogged with several bearing failures because of severe rust.
I seem not to have this problem with my YS .91AC because its lower end internal parts are always being washed with fresh fuel while running. I would guess that the YS requires extra lube because it is contiueously SP? being washed away with a fresh charge every cycle.