That was interesting as I have lived in two highly agricutural states (KS & OK) and neither has a licensing requirement or a stipulation about "farming use". Just guessing here but it seems the WI legislature had to write a law to stop the squareheads with DUIs from using tractors as alternative bar-hopping transportation in the WI hinterlands.
you are exactly correct. In fact, a distant relative of ours drove an old Case around for years because he had his license revoked and just never bothered to go and get it reinstated.
Also, there were several farm tractor accidents in a short period of time involving children driving tractors...