If you compare the box manufacturer's certificate (BMC) on a box made from 200# board with the BMC on a box made from 32 ECT board, you'll see the same gross weight limit: 65 pounds. However, 32 ECT board may be created with lighter-weight material that has been engineered to have crush resistance without necessarily having the tensile strength that gives 200# board its burst resistance. For this reason, 200# board is usually heavier than 32 ECT board, and 200# board boxes are thought to be better suited to the battering that small packages can receive during shipping.
UPS guidelines suggest that 200#-rated boxes can handle heavier loads (40 pounds) than 32-ECT-rated boxes (30 pounds).