Well, yeah. If they don't and are hauling more weight than their plates allow, the highway patrol will give them a ticket. If I wanted to haul over 3 tons of weight with my Tahoe, I'd have to have commercial plates even though it's not being used as a commercial vehicle.

Until fairly recently, all trucks were licensed with the "COMMERCIAL" rated plates in MO... Even the show truck I had in the early 2000'w had to have commercial plates, and the most it ever hauled was detailing equipment.