While what you said might be true, every four stroke fuel I've ever seen contains LESS oil (16%) than most two stroke fuels (which usually have 18 to 20%).

I believe the theory behind it is, that two strokes fire every revolution (as opposed to every other) and therefore require the additional cooling provided by addional oil content.

Paul,
I was partly kidding because you've already heard that you can add 3 or so ounces of the proper castor oil to your fuel to make up the extra 2 to 4%, but you CAN simply run the engine richer and accomplish the same thing. (At a slight reduction in power and slightly higher consumption rate of course.)
Dennis-