I'm a little fearful of the all-aluminum engines that are showing up on some products these days. Just having an aluminum head can be something of a drawback too.
But, the maintenance regimen of the owner is a major variable.
I've been lucky enough (and perhaps through frequent oil changes too
) to have never required any major engine service on anything I've owned. That includes one lucky 2.6-l GM engine with 350k miles.
It used to be routine to require a valve job in the 80-100k mile range on a gasolene engine. Somehow the designs have changed and that is not required as often now.
But you can still get a "lemon" design. We can sure expose plenty of them, even in the Mercedes lineup.
All said, just look around you. What 20-year-plus cars do you still see on the road as daily drivers? W123 diesels. I don't ever see any of the Ford Mustangs from the 1980's like I once owned. The square boxed end style that followed the Mustang II (which I also owned - and you don't see either.)
Ken300D