I agree about the body being galvanised, but have you seen what the salt does to the underside bolts, hangers, clips, brake calipers / pistons etc. If you do your own maintenance, I found that you spent more time trying to release frozen & broken bolts than anything else
I saw an article in one of the UK Porsche magazines last month where there was a step by step procedure on how to replace the fuel lines that had rusted through...
And some other poor guy was asking where he could get the pipework for his rusted out power steering connection pieces! Now thats the downside of driving in winter.
When I worked in the UK, I found it was cheaper to buy an old clunker and lock your good car away 'till Spring is sprung.