This is what the haters don't seem to understand: Krugman is not popular because he is some kind of political hack. He's popular because he thinks carefully about issues before speaking on them. He's popular because he gives credit where credit is due and then speaks truth to power when he has to. As I've said before he's a goddamned national treasure.
I understand he gets catty sometimes, but usually when you accuse him of being cruel he's actually just saying emphatically that he thinks you're wrong (which is not inappropriate at all). Even when he's genuinely out of line (we all slip into it), he's a paragon of virtue relative to much of the economics blogosphere. To my knowledge, for example, he's never written anything nearly as cruel as this, and people usually (as far as I can tell, rightly) consider that guy to be fundamentally a nice guy.
btw - these connections he's making - separating mark-ups out from rental rates on capital, and thinking about the responsiveness of investment to each component of profit - should be very familiar to anyone that works with Post-Keynesian models. This is why I don't take the Post-Keynesian griping about neoclassicism very seriously: you can get the same result with Cobb-Douglas and Dixit-Stiglitz. The value Post-Keynesians add is in the different sort of questions that they ask, not their stand against neoclassicism.