Federal Motor Vehicle Safety Standards (FMVSS) are different for vehicles of 10,000 lbs. GVWR or more. Also sometimes state registration fees are increased on vehicles with GVWR 10,000 lbs. and more.
Commercial vehicles 10,000 lbs. GVWR require a DOT number if used in interstate commerce. That brings along many regulations and record keeping requirements. That's why my former employer (interstate pipeline company) got rid of all the 1 ton service bodied mechanic's trucks and went to 3/4 ton trucks. It really handicapped the mechanics. They had to leave behind lots of tools and spare parts they once carried. That's why the 3/4 ton vehicles do not exceed 10,000 GVWR.