I've seen it. It's interesting to ponder, I suppose. My thought is that the Powers That Be, being omniscient, would have arranged to make Hell just precisely as large as it eventually needs to be. This renders the question of expansion moot, thereby nullifying the presented explanation.
A simpler solution, I think, is this: If anything is getting into Hell and nothing is getting out, then Hell is by definition endothermic.
But then, what the Hell do I know?