Don't pretend to know all the details but I do know that I trust the info in Bentleys and Probt's writings on this point. And I do place some credence on the collective experience of the more knowledgeable Brickers here on the Brickboard. I care little about peoples subjective opinions on beer and butter, but personally when I was a drinker I throughly enjoyed many a cool Bud on a hot day after cutting the grass, never did care for margerine though. Air intake preheat has been used on most makes of cars not just Volvos.
Yes of course a problem affecting startability can affect driveability and vice versa, for example a poorly maintained ignition system. But as I said the pre heat system has nil affect on starting. The preheat is only active when heat is produced around the exhaust manifold AFTER starting the engine. Them's the facts and I'me sticking to it.