If you have the money to buy a luxury car, you probably aren't scrutinizing cost of ownership as much as someone buying an economy model. Plus the dealers want the extended business and high end cars are more likely to be serviced at a dealership. Thus, high end manufacturers do not focus on reliability. Another contributing factor is cutting edge features. The motorized lift gate won't go bad in your economy car because it doesn't have one.

Japanese cars are famously reliable. German cars are not. A Toyota Corolla is miles ahead of a Mercedes S Class.

This is shocking to me. Do you have any insight? Mercedeses newer than 2010 are considered incredibly reliable here in Europe. They had a rough decade before that, but since the introduction of W212 E-Klasse, they're back on track. Is that different for USA models?

How can you call any car newer than 2010 "incredibly reliable"? There's not nearly enough data on it. I would certainly expect a car less than 10 years old to be reliable, incredibly reliable to me implies at least 20 years of reliable operation. I own 2 Japanese cars that are both over 20 years old and have over 250K miles/400K km each, one of which is a Corolla, and they still run fine.

I'm of course talking about high-mileage applications. These newer Mercedeses (specifically W212 E-Klasse) are popular among taxi drivers and often have more than 800000 km on them - and still going strong. I'm going to buy this car for this exact reason - because taxi drivers are so happy with it.

How many Japanese vehicles were compromised (and had resulting loss of use) by the Takata airbag debacle?

While other answers have touched on some of the reasons for this, another one I always assumed is that the econ-o-box car will sell in far greater volume than the luxury car, meaning costs of R&D can be spread over more cars.

I would guess a Honda Civic actually has way more $ in R&D spent on developing it than a new Ferrari, or even a relatively common luxury like a Porsche. Someone correct me if that's wrong.

Yes. Upmarket brands are known to be plagued with various electrical and "feature" problems that don't bother other cars - the lone exception appears to be Lexus, which tends to rate about as high as Toyotas.

But Acuras tend to be less reliable than Hondas

Infinities tend to be less reliable than Nissans

and so on.

Basically, fewer moving parts means better reliability in general. In addition, lower level cars are much cheaper to repair for various reasons.

Want a car that will run forever on the cheap? You're probably driving it.

I have had a 1996 R33 Skyline for 7 years, more than 100,000km and haven't had a single issue asside from a worn suspension boot. Given its age, that should be remarkable, but it is my second R33 and the first was just as uneventful maintenance wise. I am not particularly kind to them either.

The first one was rear ended by a Suzuki Vitara, which wrote off the car, in case anyone was curious why I have had two.