truth, I agree with you 110%
But a few things that come to mind to ponder, is the cop becoming your "witness" (that you are not in commerce) when you mention that to him?
They use anything you say against you, right? So maybe when you tell them you are not in commerce you can use that against them if you receive the ticket and go to court.
Also, about the DL issue, like the example of the delivery truck driver working in commerce but once he delivered the load and he is on his way back without any commercial load, he is not "driving" anymore, is he? He might still have his DL for when he is "driving" in commerce but he might not be engaged in a commercial activity all the time automatically, that is why you rebut the assumption (I guess).
There is a Florida statute like this:
The 2004 Florida Statutes
Title XXIII; MOTOR VEHICLES
Chapter 322; DRIVERS' LICENSES
322.53 License required; exemptions.--
(e) Drivers who operate straight trucks, as defined in s. 316.003, that are exclusively transporting their own tangible personal property which is not for sale.
Chapter 316; STATE UNIFORM TRAFFIC CONTROL
316.003 Definitions.--
(70) STRAIGHT TRUCK.--Any truck on which the cargo unit and the motive power unit are located on the same frame so as to form a single, rigid unit.
I am not sure why it worked, I am happy it did, I am not going to take any chances or push my luck in the future because like you say there are no "rules" with these people.