Not necessarily. If the body was kept clean, but the undercarriage was unchecked, the body would be spared the corrosion that would be allowed to settle on the undercarriage components.
Still. Frame components are treated for corrosion, simply because they suffer the most exposure (and subsequent neglect).
I would believe that since MB touts the safety aspects of their vehicles, that they would design critical undercarriage components to be fairly bulletproof and those parts most suseptible to corrosion to have been treated likewise at the factory.
After all, these cars come from Germany, where the weather conditions during winter are not like LA.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car