Hmmmm.....the area where the photo says "Small rust spots" is close to the underside of the bumper. That's an area that would be hit by road debris, stones, etc as you drive. As soon as you have even the smallest perforation of the chrome, the rust comes. Not sure if this is actually an issue or not??
When I had my 1997 F-150 you may recall (or not) that the exhaust pipe exited just in front of the passenger rear wheel. They found out that the exhaust fumes corroded the rim and the lugs. My rim and lugs were replaced under warranty and the exhaust pipe was routed to behind the wheel under a silent recall.
**Edit..I just ran over to the neighbours 2006 Chevy pick up, and he also has small pitting/rust on the underside rear bumper area. So if this is caused by rock chips, and then road salt getting to where the rocks have chipped, I guess the only way to fix it is to have thicker or hard chrome??**