Jim,
I agree with you 100% with what you are saying. But what I am saying is, there are local building inspectors that will reject wiring in a "home environment" if the breaker does not match the wire size. OR at least the wire size is equivalent or larger than necessary for the breaker size. If course, the inspector will want to check out your motor protection at the control panel on the machine, too.
Personally, myself, I oversize the wiring by one size just to eliminate problems later down the road. And some day after I'm gone to the magic machine shop in the heaven's, The new home owners won't be left with a mess to deal with, just to get the home insured or to pass inspection when they find a 12 ga. wire tied to a 30 amp breaker. And the other end of the wire ends in a junction box, worse yet, hanging down from the ceiling, not connected to anything.