A comment in the "horse barn" thread has stirred this question. Can you run NM in conduit for any significant distance. My understanding of 336-6 (and now 334-15) is that conduit protection is used in short runs for specific hazards. Because NM is a cable assembly and not just conductors, running it in conduit is "mixing wiring methods", and you're subject to overheating.
I don't see how heating is considered an issue at all, code wise. You derate the same in 1/2" conduit as you do in 4" for the same conductor fill. A piece of Romex in "free air" EMT will certainly run cooler than it would buried in insulation in an attic.
the .22 additions only point out rules that always existed. Basically you use the widest dimension of an oval cable as the diameter when computing fill. That is because when you get a twist in it the widest dimension becomes the diameter.