There was ample post discussion beyond the quote.
As mistergreen suggest....some tap will have more, and some will have less CO2........surface waters will almost all have lower CO2, well waters will generally all have higher CO2 content.
Some might provide a limiting nutrients, other tanks might not have any limitations..........
In each case, there is a good chance that the aquarium looks better after wards.
O2 is almost always higher with tap and vat/reservoir water vs tank water unless it's done the latter 1/2 of the light cycle.
The other hypothesis is perhaps O2 demand by the tank water and consistent export of that, leaving more O2 available that would otherwise be used by micro inverts and bacteria to break down organic matter/waste.
Which could explain a lot regarding daily automated water change systems.
I've installed a few and they seem to be without any issues over long long time frames.
The gas film issue could also provide some insight/support into CO2 mist hypothesis.