I see reports of this too, but I have three recent MB cars (the oldest is
December 2004) and there have been no problems with any of them apart from
the C Class which had a damaged supercharger (damaged in the factory during
fitting) that had to be replaced under warranty.

I know that the surveys that are done in the UK tend to rely on people
reporting faults and I suspect that MB owners expect more and are likley to
be more disappointed when a fault occurs and therefore more likely to give a
bad review.
I know that MB in the UK looked into the problems and found that a lot of
the disatisfaction was dea;er related with the big groups for whom MB was
just one franchise of many not giving as good customer service as the
smaller specialist dealers.
I think I have been lucky in this regard because although the dealer I use
is quite large and has a lot of branches they only sell luxury brands and
they do have quite high standards of customer care.

My A Class has done a high mileage and not been well looked after but it has
never had any faults. The SLK has been trouble free too.
I like the C Class a lot but the boot is too small so I am swapping it for
an E Class. Having so many cars means that none of them do a high mileage
and I never keep them long enough to need tyres or exhausts.