Most of the newer 4stroke engines use a semi dry sump anyway. They use the windage off the crankshaft to force the motor oil in the bottom end to "sling" through a small opening and into another section of the case that's where most of the motor oil is contained. Windage actually doesn't care about gravity either...so as long as the engine is running (even in "zero G" free fall after a huge jump) it's clearing the crank case of excess oil.
Now, there ARE 4 strokes that are designed to run even inverted... Some aviation engines have crankcases with cylinders located below them (look up radial engines). Oil squuzing out of the rod bearing journals will generally tend to "fall" into those cylinders but they're not really any more likely to burn oil than the upper cylinders because the crankcase is specially designed to "catch" the oil that the oil control ring on those bottom cylinders "pushes up" while the piston is actually "falling" inside that cylinder.
There is even another even more special class of 4 stroke engine that is designed to have no excess oil in the bottom end at all. Handheld 4 stroke engines are designed with a scavenge pump buil in that picks up any oil that's located in the crankcase and small "squirters" that spritz oil up onto the rotating mass. The bearings are all designed so that the "spritz" is enough to keep them happy....
and yeah most of the 450 2strokes quads which you see doing flips are dry sump and have a seperate oil tank...
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