henry is a smart guy. i ran into him first on rec.audio.tubes around '98 or so. worked for bell research for years. funny how some of the smartest guys i know worked for the phone company... or at least used to.
as far as the effects of heat on the electromagnetics.. you're right that as the heat goes up, the DCR of the windings will too, and that will change the Q... BUT whether or not that makes a difference in the spark energy depends on whether we're talking about a tuned circuit in the first place. i really don't know whether or not they're taking advantage of a sort of multi-spark bounce that could occur if the circuit oscillates.
i've got an LCR meter on my workbench so next time i change plugs i'll get some numbers. hmm, should be in around 8 months now..