Things like zinc additives do help add kind of a lubrication effect because of the "softness" of the way the zinc attaches to the engine parts, but this effect is dwarfed by the actual lubrication effect of the oil.
On the dark oil, birds said pretty much everything I thought of lol, he has a habit of that , but he's very right that it takes a tiny amount to stain the oil black, and that the oil absorbs the carbon into it's structure, the carbon can't really escape this to build up anywhere. The oil can take an awful lot of carbon before reaching saturation. It's not like once the oil is resting after a change the carbon all falls to the bottom of the container, it stays in the suspension because of the particular physical chemistry effects the designed additives have.