I had a top rail rust from salt, I believe. Notice I said A top rail not MY TOP RAILS. I ran a salt pool for 6 years, then I switched to salt. 2 years after switching, one of my top rails developed rust. It was where a volleyball set up rubbed against it and damaged the coating. This is the only spot that developed rust. In all likelihood it would have developed rust without salt as well, maybe a tad bit slower. The point being, it is the quality of the pool and the integrity of the finish that prevents rust. Not the presence of a small percentage of salt or not. I spend enough time around my yard painting, sealing, staining, etc to realize EVERYTHING will degrade over time from sun and rain, no salt necessary.
My biggest issue with salt was that I used to have an overflow on my pool in the skimmer. It ran under my pool deck and drained onto the grass. It kept the pool from getting too full when it rained. When I switched to salt, it eventually killed the grass in that spot.