Why cars rust

WildCat said
the new spray on ice preventer is more corrisive than salt.

the comment about keeping one clean and doing proper maintenance is correct to a point. But if you drive a car on salted roads there are places you cannot get to and that is where it will start to rust.

Oh no, my Mustang is rusting !!
Had to go to Ohio on family business in Dec 08 and this is what my car looked like after 3 miles of salted roads. The Interstate was dry.
The next morning it went to the self-serve car wash and got the bottom flushed out after being jacked up. Then it rained for the next week so the car got completely flushed.
1000 miles of hard rain will get any salt out.