I think that a lot of it has to do with luck. I had an 02 silverado, when I sold it the only rust was on the fuel door. Of course I washed and waxed the crap out of the truck, but I don't think that mattered much. My dad never washes or waxes his 2002 avalanche and it has little rust. I have a friend with an 2001 silverado. The bed is so rusted that it flops around while driving at any speed. The rocker panels are eaten all the way through. My brother had a 2011 quad cab silverado. After one year the rear door sills were rusting. Rusting to the point that the weather striping was peeling off. He took it to the dealer and they said sorry, it is not rusted through. He laughed and said, "it is a lease, not my problem, all yours next year". They fixed it!
To be fair with mine, I bought it with rust on it. Previous owner lived in CT and traded it in when he moved to Va. Northern Va salts their roads too. So my truck has lived a salty lifestyle lol. I'm in Cali now so I plan on removing the rust from the frame myself with my good ole Navy skills and know how haha. And I'm leaving the body paint to the paint shop lol