Agreed, but you've lost me again - I don't see what that has to do with what we're discussing? The air pumping through your airstone is the same as the air at the surface of the tank.
I'd imagine the surface area of all the bubbles combined greatly exceeds the area of the tank's surface, therefore the gas exchange of a bubbler exceeds the gas exchange at the tank's surface surface, and the benefit is direct gas exchange by the bubbles, not just increased surface agitation.
Vaguely recalling high school physics, I'd have thought you'd get more gas dissolving into water if bubbles are at a higher pressure than ambient atmospheric pressure? But then I don't think bubbles would be at a higher pressure in just a meter or so of water anyhow.
BTW, sorry to the OP for the hijack :oops: