Sure, the number of existing PC players who'd want a controller for some games might be miniscule. But that's why they choose to game on PC. For others, where the subjective preference for controller type happens to prefer controllers, a (perceived) lack of support on PC for their controller of preference is going to discourage their migration to PC.
All things being equal *I* prefer a controller to mouse and KB since I sit in front of a computer all day at work. Given this, I can only think of the one case (Mass Effect 3) where a game on PC didn't support gamepad controls and where I didn't feel that KB+M controls were a much more natural fit for that game. And, since I had the choice, I bought that on 360.
I have to admit, I'm kind of lost as to who the subject of the thread is. A hypothetical average console owner or you personally? A lot of the issues you raise seem to revolve around your personal preferences, but then you have used language to indicate you're speaking of the group of console owners as a whole. I see a marked difference between the former and the latter.