How come? Brother-in-law has been doing 30-40 000 km per year on a Ford Mondeo for years, much of that on dirt roads. It is of course to be expected that worn-out parts have to be replaced, but we should not need to worry about road safety based on mileage, even if driving on dirt roads.
Luxury cars are a lot heavier, putting more strain on the suspension on rough roads. Also, a bad ball joint would have shown up as loose steering when the tyres were being changed - I'm surprised it wasn't picked up earlier.
Not that much heavier. Current Ford Mondeo, the boring, economical workhorse, has curb weight ~1550 kg, MB E-class is 1600-1800 depending on model (engine and drivetrain). Tesla Model S is further away at 1960-2240 kg.
However, what's essential is that in car design, you of course dimension the parts so that they match with the expected load. It is totally not acceptable if the parts cannot take normal use and become dangerous, and driving on dirt-surfaced roads is normal use.
Off topic, but I'm always surprised by this kind of considerations. Over here, cars have annual inspection similar to the British MOT test (except new cars only on 3rd and 5th years) and there the engineer checks anything that has to do with traffic safety. Americans drive newer cars (average 11.5 years compared to our 13.5 years), but apparently maintain them less as there are no mandatory inspections in most states, beyond some smog tests.
Over here, people change tyres twice per year (winter/summer wheels) so there's an opportunity to look at brakes and suspension.
