Not necessarily it can be down to design. When I had my first motor mover a Reich I was seeing weights between 31kg and 37 kg for different makes all with ostensibly similar capacities of weight v incline.
It is just down to the makers slightly different designs and possibly materials. I suppose it is why a Mondeo weighs a different amount to an Insignia. They both do the same thing, but the manufacturers do some things differently.