I remember it had to do with a couple things, one being that most skimmers are trapped under a sump (such as mine) and so the skimmer never getting any "fresh air", and just recycling it over and over.
And then it said something about just because you have bubbles under water doesn't mean that the water is injecting o2 and that the water can not release co2.
It mentioned bubble size (Uber tiny), the way the skimmer forces the bubbles up and out, How Salt water is different than fresh when it comes to gas exchange, and where the skimmer gets its air.
I know what you mean though, I was in your camp, till I read the article.