It's a pretty safe assumptiom. In the current production world many standards have to be achieved and engineering costs certainly assist with the retail value being assigned. What value would it achieve to have different suspension pieces and many other bolt on parts for basically a biscayne vs the impala ? It's not like one is a 1/4 ton and the other a 1/2 ton unit. The 1100 has a few more hp due to the fact of the heavy cab. Driving four wheels in a soft earth situation takes more hp with the added weight. It comes down to the basic open air or the deluxe enclosed temperature / noise controlled atmosphere. The dealers would have to stock many additional parts which for the same basic machine would be costly.
My friend optioned out a new diesel truck... a heavy 3/4 vs a 1 ton. After getting the specs including frame thickness, transmission, rear axle, body , radiator, coolers, ( and the list goes on........ the only difference for the price difference was the spring package. They can't completly recertify a truck with all new different components without massive costs and tests.
So... you be the skeptic, I will use common sense.