From what I've seen, which isn't much:
The BMW's weren't quite the luxury mobiles we see them as today. My E30 convertible has vinyl seats, a manual top, no climate control (just hot or cold knobs), nothing can really go that wrong. Its pretty simple.
The Mercedes on the other hand were luxury, at least in the US. Almost all of them were loaded to the gills, a whole lot of sound deadening, climate control, etc. etc. I have a friend here who was born and raised in Germany and studied with Mercedes. He recently bought a 190e (not running) and is debating what to do with it. He doesn't like it because it doesn't have crank windows or even the option for it, it has too much sound deadening, etc etc. Its waaayyy heavier than it was in Europe.
In short, whereas you could get a pretty base E30 in the states, you could not get a base 190.
This might be completely wrong, take it with a grain of salt.