You asked a question on an international forum. The odds of finding someone from Massachusetts, let alone someone with in-depth knowledge of MA's DOT laws, is slim. Of course you're going to get answers that don't exactly answer your question to your satisfaction, and here's one more:
Don't complain. In NY, you need commercial plates if the vehicle is something like 6200lbs unladen. Years ago, if it wasn't a car, you needed commercial plates. 1/2 ton pickups, Ford Broncos, Chevy Blazers & Suburbans; all were licensed as commercial, period. I don't know if it cost anymore because I was too young to care about such things, but I never heard the folks complain.
