However, in the USA, it's rare to find a BMW 7 series, late model, with the V8 engine to last much longer than about 200,000 kilometers. Statistically, they have fairly poor reliability after a certain point. The V8s in particular are known to leak oil and have various problems.
Makes me wonder how reliable a Rolls Royce would be, but then again, maybe the people who own those don't keep them after they're a few years old and when the mileage starts getting high. Rolls Royce is owned by BMW and is a technology partner with BMW. Thus, some of the car's mechanical and electrical architecture is somewhat similar to BMW's.
But I always had the mentality of buying something extremely high quality, thoroughly using it (cars for many years and ideally lots of mileage), maintaining it well, and making it last. Seems like a Mercedes S-Class might still fit the bill. But I've already found out through personal experience that it will cost a lot more and take a lot more of my time to get a BMW to 200,000 kilometers than the equivalent Mercedes.
But going back to your point. Yes, you're right! Reliability probably is going to be good since it's a Mercedes S-Class. And you said S-Class, not BMW 7-series.