I see rusted out older Ram trucks constantly around here (SW Ohio). Doors, tailgate, front and rear wheel wells and the rockers. Most are well over 10 years old though. 7 years just isn't that old for rust to start showing up on any exterior panels.
My truck is now 4 years old. In 3 years, my truck will not have any holes in the rockers or any other sheet metal either- but, give it ten more years and it will. If I start to fight it now though it'll be one of the few 2013s that's not all rusted out down the road. I managed to stop a lot of it on my old truck with rust-converter, but it was really too late at that point. Trying to stay ahead of it with this truck.
I will agree that rust depends on the manufacturer and how it's built. I've seen some cars owned by family members that were 15 years old with no special treatment, and they looked perfect underneath. I think it's got more to due with the manufacturer properly painting the bottom and the cavity portions of the vehicle than any coating the metal gets before paint.