Acid rain is actually a problem, even in some areas of CA. A new car that I bought was damaged by acid rain shortly after I bought it (new car bad luck strikes again).
The worst is actually drizzle that beads on your car, and then the sun comes out, with the water drops acting as magnifying glasses resulting in much heat. This causes a chemical reaction resulting in acid which leaves marks in your clearcoat when the drops dry. Sometimes the rain itself is acidic from polution, and sometimes it just mixes with some dry acidic dirt particles that fell on your car separately before the rain.
It's quite nasty when this happens. I typically try to keep at least my hood, roof, and top of the trunk clean. Also, I try to wipe drizzle water beads when I can before they dry. Obviously, I can't always baby the car like this.
By the way, cars get damaged, and there isn't much you can do about it really... Stones hitting the windshield hard on the highway and leaving marks (or worse - chips and cracks) is another type of unavoidable damage that I hate. If you ever see how they replace windshields, you'll understand why that's not something you want to end up having to do...