It would depend on the type of oil and additives. Maybe they use a type of oil that is more easily burned and therefore doesn't effect the engine as much.
As oil technology has increased, there have been better oils introduced into the 2-stroke world, allowing you to use less oil with the same amount of protection. This is especially noticeable in the dirtbike/4-wheeler/snowmobile world, which I own all of. My statement above is of my own findings from dealing with and maintaining larger 2-strokes engines, and would still apply to the smaller (R/C) engines.

The Trinity 18% is made and recommended for break-in procedures, but can also be used for the backyard basher who doesn't care as much about performance, and who would like a higher oil content fuel.