[Giller]

I would argue it's not the snow or the ice but the SALT that gets spread all over the place that does the most damage. Even a car that's parked - if it's left to sit outside, salt will find it way to the underside as you shovel around it and such. Salt is everywhere in the winter. The garage at least keeps it to a minimal (still gets tracked around on your boots and such).
I would encourage anyone who parks it for the winter to find an indoor spot. In my neck of the woods, there are a few places around (Farms) who have large sheds that they rent out in the winter. For less than $250 - you can have a dry, insulated place to store it. And that's 250 for the season! And trust me - many of these sheds are housing $100,000 tractors and such - so they are kept clean and tidy.