Newtonian physics, ya'll - a body at rest tends to stay at rest, while a body in motion tends to stay in motion - it's called inertia. And guess what, it's proportional to the weight. (Sorry, the engineer in me had to be let out!)
When I had my deck rebuilt several years ago, I picked out the spot where the grill was going to go (the POSK at that time) and had two things done - shortened the joist spam for extra support and that corner of the decking is ironwood, which doesn't burn. It will scorch, but not combust. While the KK 23" does weigh a bit more than the old grill, I haven't noticed any support problems. These are industrial grade casters, so they will never get flat spots.