They don't seem to rust proof them very well. It's even worse on imported cars.
I bought a new MX-5 in 2007. By the time I sold it in 2011 the rust on the underside was shocking. After just a couple of years many of the bolts were rusted on so badly they had to be drilled out and replaced just to do a wheel alignment :/
Aparrantly, you simply do not get old cars in Japan so building them to last is not an issue.
Most modern vehicles seem to be very poor in the rustproofing dept.
I have said before, it is almost "Back to the Future, 1970" when the manufacturers only painted the bits you can see.
I blame the CO2 obsessed.
Manufacturers are shaving off every "Unnecessary" gram, hence no spare wheel, cooling systems with only 4L of water, sumps with only 3L of oil, windscreen wash bottles that only hold 1L of water so you are always having to top them up, and so on.
And of course, No underseal!
(Underseal is thick and heavy, not using it probably shaves as much as 10Kg off the cars weight)