The further North and the more salt you get, the more likely broken springs can happen.
The stock springs have been dipped into a plastic coating to keep them out of the elements, at least for a while. The springs are high carbon steel and it's not that they rust, it's that the rust will follow any carbon striping (inclusions) in the spring steel. Any inclusions, which are not uncommon... and a few years of working into a weakness in the steel, a good hard jounce or overload, and the spring breaks.
It's one of those 'whatever it takes', situations. It's not the kind of thing you can effectively maintain. I guess you could recoat the springs when you are doing shocks. There are good suppliers of aftermarket springs. Be aware, there are usually 3-4 dots of color on the springs, which indicate the car and load the springs are intended to take. New Beetles springs aren't the same as a Jetta Wagon.