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.I'm just looking at motor movers, and I've found that they all seem to vary in their weight.
Does the weight matter?
And what is the difference between a heavier motor mover and a lighter motor mover? I'm guessing the heavier ones are made to move heavier caravans?