Very true. 4WD, extended/crew cabs, etc all take away from towing capacity. Sometimes a 3/4 ton will have more towing (but not hauling) capacity than a 1-ton for similar reasons, but usually the difference is small.Actually a extended cab takes away from the towing capacity in all trucks I have seen. You usually get your highest towing and payload capacity in a long bed regular cab plain work truck. They are the lightest and that = more capacity.
Chris