Don't forget the failures possible in surveys -- it is quite possible that brake pad replacements are causing the low rating, as most Japanese cars don't need them for 60,000 miles or more (a friend of mine got 120,000 miles on the original pads in his Toyota Avalon -- they actually outlasted the car since he got broadsided in it, drunk driver ran a red light. He does drive like an old man, since he is one, but still.....), while a Benz may need them at 20,000 mile intervals in heavy city driving. Dust on the wheels will cause all sorts of racket from the gated community crowd, since anything less that showroom new look makes them feel cheapened, sorta like they actually WORK for a living or something. American cars don't make much brake dust, and the fancy wheel covers hide what the do make.....so no "complaint".
Hummer H2s are getting enourmouns numbers of complaints, so they would rate very, very low -- and guess what they all are -- bad milage! Now who would be surprised that a 6000 lb 9ft wide knobbly tired square lump would't get better milage than the 6/8 mpg on the window sticker? But its still a "quality" complaint.
German cars require much more regular maintenance than a Japanese car that usually only requires oil changes and tires, everything else lasts 100,000 miles these days. MB's will require more regular maintenance, at more expense, but then you still have a better car at 200.000, at which point many of the Japanese cars have fallen apart. Age counts more than milage, unless abused, I think, as the 1990 Nissan I'm stuck with at work runs fine at 232,000 miles, but the suspenstion is gone -- shocks bad, bushings bad, etc. May be a real expensive fix at this point, while a Benz isn't too bad.
That said, the news from MB dealer serivce centers in big cities is that the newer ones are MUCH less reliable, and prone to very expensive failures. BMW and Audi ditto, it's mostly the electronic controls.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!