> 1) Cars have had baked-on finish for 20+ years and generally don't rust through anymore, even with the ice melt put on roads in Minnesota;
If only the primary corrosion problem on automobiles were the painted unibody, which still is only a minor scratch or collision-repair away from devolving into the same rotting trash.
Especially with newer vehicles employing more aluminum parts, often fastened using steel fasteners if not to steel surfaces, you get plenty of galvanic corrosion at these critical junctions. The dissimilar metals exposed to saltwater electrolyte is basically a battery. And this is occurring out of sight unless you get under and wrench on your own vehicles, where there's substantially more exposure to the road salts.