Sorry, but if that were true, you wouldn't have any frame rust. More likely you washed the body as needed, but didn't even think to wash the undercarriage. Ignorance is no excuse, it's still neglect on your part, intentional or not. It is however a good learning lesson.
I reply to most of these threads, because I think people should take responsibility for their actions, or in the case of a rusted vehicle, inaction.
My soon to be 18 year old 4Runner (which I bought new off the lot) has spent it's entire life in a State that salts the roads heavily, all winter long.
I knew what the salted roads can do to any make or model of vehicle, so I determined to be very proactive in washing the salt off the entire truck as needed. I've spent lots of time with a garden hose, washing off the entire truck, including the undercarriage, in below freezing temperatures, in the dead of Winter.
A neighbor used to make fun of me for doing that. His Mercury Mountaineer, (fancy Ford explorer) which was the same year as my 4Runner, was neglected during the Winter months. It was hauled off to the junkyard years ago, because it had rusted to the point of being unsafe to drive.
Bottom line: Even a neglected 4Runner will last well past the rust warranty period. If you want it to last even longer, it needs to be maintained. In a highly corrosive environment, that becomes far more critical, no matter the make or model of vehicle.
