We can't be too cheap, though. There are certain markets with a mandatory 10 year corrosion warranty requirement, for example. And there are other areas that are pretty much desert all year long. Depending on the particular destination market, we absolutely do build cars differently. In the vast majority of cases the processes are identical (e.g., ecoating, sealing, paint), but we'll use different coating weights (maybe bare for the Middle East, and 50g/cm^2 for Europe) on particular parts (e.g., the roof panel). Coatings (hot dipped, electro-galvanized, etc.) are really just an insurance policy. Sealing and ecoat are obviously the biggest contributors to sheet metal life, as well as drainage.
This latter is something people don't think about often. Your modern car has all sorts of intentional drainage areas that stop your car from rusting. Unless they get plugged up. Then dirty water accumulates, and it's not pure, clean water. It's stuff that will eat through paint and start causing premature corrosion problems.
We don't have to be vain about washing our cars, but washing our cars (especially in winter if snowy/salty environment) is just as much about making sure all of these drains stay free as it is about making the car look nice. And I mean a full, spray wash, not just a bucket wash on the exterior surfaces.