Right, but by that reasoning if the rules read that you can lift/drag x lbs, you shouldn't need to make a check to lift/drag x lbs.
It's not practical from a DMing standpoint. How often do you hear DMs complain that their players never retreat (when these kinds of checks could well be the reason why).
It's not even especially realistic. Both soldiers and firemen have heavy kits and are trained to rescue comrades wearing similarly heavy kits. So my level 20 fighter with 20 strength is inferior to a real world volunteer fireman? It's because the DM just decided, in the heat of the moment, to err on the side of caution, because martial.