Good answer.
I would have worded it in reverse to make the point more clear. The purpose of the torque is to get the clamping force correct. It is correct that that should also stretch the bolt the correct amount in order to meet the primary goal, the clamping force. How much the bolt stretches, or whether it goes into yield or even fails, is determined by the size of the bolt. So first you pick the force, then you use that to pick the bolt size. And that is why you see eight sizes of bolt on the same lawnmower - it's not really to make you buy eight different wrenches, that's just a side benefit.
You also alluded to the difficulty of getting the accuracy. From what I've seen, nobody with a torque wrench does any better than 50% plus or minus his desired amount of torque, so which end you put the wrong torque on is probably moot.