The MB USA brochures for both the 2002 C-Class and the 2002 E-Class have exactly the same description for the FSS system...
'....The Flexible Service System in your Mercedes monitors the oil quality, engine loads, RPM, operating temperatures and driving habits to determine when regular maintenance is necessary.'
This covers not only the 3.2 liter V6 and 4.3 liter V8 but also the 2.4 and 2.3 Kompressor engines. They all have the same system.
The M-Class brochure says something similar but not in the same words.
The FSS system needs the ability to measure the quality of oil in order to identify if and when the oil is changed between resets of the FSS system.
I'd guess that if a vehicle has the FSS system, it has the Mercedes/Shell system to measure the capacitance of the oil, hence the quality of the oil.