> a great deal of the benefit of salt comes from friction as cars drive over it
You may have never tossed a handful of rock salt on steps that have a quarter-inch of ice on them and watch holes actually form in the ice within a half hour or so.
Again, it's temperature dependent. Salt lowers the freezing point of water about 4 degrees (either units). Typically when it snows, it is close to freezing (if warmer it would rain, if much colder there wouldn't be enough moisture in the air for precipitation) so adding salt will melt the ice, but there's plenty of time when it's not in that narrow temperature range.
You may have never tossed a handful of rock salt on steps that have a quarter-inch of ice on them and watch holes actually form in the ice within a half hour or so.