At the Chicago show this year, there was an American pipemakers forum with Michael Butera, Lee von Erck, Jeff Gracik, Adam Davidson and Joe Nelson. Someone asked a question on finishes and, to paraphrase, they all agreed that briar does NOT breathe and that a particular finish blocking the "pores" of a pipe is a myth. So they're in agreement with Stephen Downie (which is what one would expect.)
"It seems the rust allows the heat to disperse faster due to all the pits and grooves in it"
I've heard this before, jsiddle, but I can't say I've ever experienced this myself (in almost 25 years of pipe smoking). If you've experienced this for yourself, well... that's quite remarkable. I'm not picking a fight, I'm just a bit skeptical.