Terminator Statism

Reflecting on Terminator Salvation, I think the underlying implausibility is seeing the struggle unfold in a world that is battered but otherwise fully operative, able to provide fuel for the resistance helicopters and steel for the Terminator forges. As it is, the Terminators would seem to run into resource constraints pretty quickly. I'm not saying that they couldn't get the WA mines working again, but that would involve having terminators that were basically civilians, driving dump trucks and the like rather than throwing people across the room in that terribly unlethal way that seems to be their only fighting skill.

But then, why do you have big terminators anyway? Wouldn't having more small ones be better at wiping out the human race? Or, even better, gas, radiation, or genetically engineered swine flu strains, not requiring any big iron at all? The only reason I can see for Skynet insisting on robots is that it was after all for a time part of the US Defence Department, and it may have been corrupted by having to process aircraft carrier accounting.