Originally Posted by
crash66
I think the other responders have mis-read your question. I don't know the real answer, but perhaps the molecular structure of CO2 allows more gas to be compressed into the space of the cartridge than plain air, which is mostly Nitrogen (I think), then Oxygen, then minute amounts of other gases, including CO2. If more gas can be contained in a smaller space, then you've gained some efficiency in packaging. Just my theory, have no idea whether it's accurate.
You got it right on the money. Molecular Nitrogen (which makes up the vast majority of plain 'ol air) is a much larger molecule than CO2, thus it's dang near impossible to compress a useful amount of it into an itty-bitty cylinder. This is also the problem with CO2, since it's a smaller molecule, it bleeds out through the rubber of an inner tube more easily.