Norm,
You make a good point. DanG nailed it, but you are corrcet about the oil.
Todays oil has little, or no, zinc. Zinc was the biggest friction fighter in oils of the past. Some oils, meant for diesels, still have some zinc in them.(Different EPA regs, I'm told.) Regular motor oils are not the best option for small engines, like Briggs.(They use flat-tappet cams, etc.)
Synthetic oils are slickerer,(Thats a technical term.)and of course additives, like you're talking about, will reduce friction.(Thats almost like free power!)
With synthetic oils, you can also use a lighter oil and have the same protection.
I have seen the difference between oils, in racing engines on the dyno.
I have seen changing oil (still the same weight oil) gain 7HP. Going to a lighter weight is another small gain.
OK, I've rambled enough. I'm not even gonna start talking about fuel atomization.
Later guys.