It just seems to me that people that inject more or less pure co2 into their tanks just gloss right over the fact that the air they breathe also has co2 in it. Wouldn't a standard air pump/stone still get co2 into the water? Just curious.
No. CO2 needs to be difffused into the water, either via reactor, or diffuser. Bubblers are far too aggressive, and will aid in gassing off the little co2 in the air. Also, you will have 0 control over the CO2 levels in the tank, and if you aren't home, or near the tank and breathing, the co2 levels will plummet. Planted tanks that utilize CO2 need to be able to closely monitor and adjust the levels of CO2 in the aquarium.