> no less susceptible to stains than stainless kitchen appliances, which easily develop grease and water stains

Stainless kitchen appliances that I've owned were pretty stain-free. That is, water, fingers, etc. left visible marks, but they were easily wiped away. There are no rust or permanent stains, IME.

They aren't used outside, but could that material be used for a car?

Also, weren't the Delorean cars in the 1980s made of stainless steel? Did they rust?