Yup, muzzleflash, in our full-scale world, what you said about the cars landing at the same time (if dropped from the same height) obviously is true. As I said, that's physics in our real world.
But as Claymore68 noticed, for a scale model "to visually appear" to be obeying it's "scale" laws of physics, we have to slow down our full-scale time to correspond to "scale" time, or that 1/100 car will look like a toy plopping off the couch if you observe it in "real scale." Which of course, is what it is.
So, it's all relative! And visual!
In that case, is it relevant to even consider scale weight? It sure is interesting!