Poor analogy, yes. But I don’t think I’m making a poor assesment of added cost of a PC addition to the games initial offering. They were already in a big budget. The design and test teams could be the same or nearly so. That leaves a port team for the PC, which could even include resources from say, the Xbox developers. Or the fact that your studio probably has those resources from other teams already on your payroll. Sure, there is indeed an added cost for the platform. But my whole point is, why kill off part of a potential market share when you’re on a AAA budget?
I’m not sure what the budget for Crackdown was initially, however.
EDIT: Doing some random reading, the rumor is that the code was a mess for RDR. So in that situation, a port would have been too cost prohibative to port, as the mess would have to be straightened somewhat. I’m not sure how much I believe that rumor, however, since the game ran fairly well on two other platforms.