I would say that lack of innovation, better testing and simpler components. European brands are more skewed toward expensive and pricey. Other than VW and some of its captive brands, everything else is $$ and aimed upscale and Germans tend to want to make things sophisticated, i.e. complex. Mercedes' cars were as reliable as a wood burning oven when they were simple. No electronics.
The Italians just never cared about reliability so they didn't even try. Why should they when customers come back year after year, with checkbooks in hand for a car that may or may not run hot and stall....yet it sounds, drives and looks like nothing else on the road.
Ditto for the British.
Japanse cars cars are superior when it comes to electronics and their drivetrain, specifically the engine and transmission. Beyond that they're not perfect. Their bodies turn to s__ after some hard years/miles, the suspension is almost always shot and the interior looks a mess. European cars hold up better in these areas in my experience, but their electronics and transmissions don't last.
People will say a Honda or Toyota will "run forever", and it will, but its POS while doing so. The interior, paint and suspension is shot to hell.
Also, not all Japanese cars are cut from the same cloth. Nissan still isn't as good as Honda or Toyota in the longevitiy race, and you can forget Suzuki and Mitsubish, they simply don't hold up as well, again all of this in my experience.
A Toyota Corolla is dead reliable because it uses and outdate gearbox and engine. It is still using a 4-speed automatic in 2012!! It damn should be more reliable. Ford is using a dual clutch gearbox in a Focus! Dodge is also in the Dart, so of course that tech is more prone to problems.
Only in the area of hybrids did the Japaense, namely Toyota innovate and push the boundaries of technology, but even then they perfected it. Prius is more reliable than a lot of non-hybrid cars per the surveys, amazing accomplishment.
M