That's Jalopnik, a site that has decided that every single part of any German car will fail every five minutes and will cost $1 million to replace
They are essentially correct. Check out for example the typical longevity of and replacement cost for the vaunted S-Class air suspension. The parts are still too new to chance getting from third parties, so you have to go to the dealer. If you don't have a very good relationship with them, you're into thousands per corner.
despite the fact that their conclusions are mostly based on a small number of American-market models with a very shady service history and lots of aftermarket parts
You should be able to buy aftermarket parts. If the design requires insanely fancy-pants parts, it's not a good one. For example, the chain tensioners in the 40V 4.2 liter Audi V8. The 32V engine doesn't have VVT, so it doesn't have them, and it's considerably more durable as a result. Both have the same stupid Flennor/Gates timing belt with a 60k lifespan. California mandates that timing belts have a 90k lifespan, Audi said "sure whatever" and rated it for 90k. It's the same belt. Chains or gears forever. But that's apparently too noisy for luxury. I'd be better off with a LS motor, which has none of these considerations and yet is just as efficient.
in the real world, German cars tend to be the most reliable
They tend to be the most expensive. That is, they require a lot of dollars invested to make them reliable. I've got a full service history on a 1997 A8 Quattro to show how and why that is the case. In spite of that I've been going through an epic to transfer its transmission into a 1998 that I got as a parts car. It's got half the miles on it, and it's in nicer condition in general inside and out. If I weren't capable of doing this stuff myself, it would make more sense to just buy something else, because it would cost too much to have it done even by an independent mechanic to justify given the low, low value of the vehicle. And its value is in turn low not just because of its age, but because of the expense in servicing it.
The average person would love to be driving something like this around now that it's been handed down from someone who could afford to absorb the expense of its initial depreciation, but they can't afford the maintenance to keep it from disintegrating. It's two hundred bucks in crankcase vent breather hoses I worked around with silicone hose and a right angle fitting, and thirty bucks for a little y-shaped vacuum hose I went ahead and bought, and the headrests don't go up and down because the drive flex cable jacket stretched over time due to heat cycling and has to be shortened and the rear sun shade has come unglued and is catching on the rear parcel shelf and the arm rests tend to crack and Audi would like a thousand dollars for one but you can often pick up a pair of them from the facelift model for a couple hundred and the list goes ever on and on.
I've been talking about Audi for a long while, but I also own a 1982 Mercedes-Benz 300SD (W126) and guess what? Mercedes is doing its level best to kill off the platform. You can get basically all the parts for cars which are older than the W126 from the Mercedes Classics parts program, but there are a number of parts for the W126 which you can no longer get new from anyone for any price. The primary example which is going to kill off these cars is the locks. Mercedes does not sell ignition locks at all any more, and an otherwise fully matched lock set will set you back painfully. No one is re-keying these locks or making fresh keys, either, but that doesn't really matter because while it had at the time the strongest column lock ever devised for a production auto, the lock itself is beyond flimsy. It also only took me about an hour and a half to figure out how to remove a completely failed and jammed lock and column locking mechanism from my car and then do it start to finish; with practice you could get that down to a few minutes, so it was really never actually any kind of useful theft prevention. But I digress. There are lots of other parts Mercedes doesn't supply any more, and the ones they do supply are now beyond outrageously priced. You can get new door seals, but you can't get new windlaces and those are falling apart and their fabric typically deteriorating. Etc etc.
Don't get me wrong, I enjoy reading Jalopnik, but you have to take some things with a lot of salt. It's directed at an American audience and they have a lot of strange prejudices and many in-crowd jokes.
They're not wrong about used Mercedes, or luxo-barges in general. It is axiomatic that there's nothing more expensive than a cheap Mercedes. Indeed, I am finding Audi parts and tools to be much cheaper and more available than Mercedes ones, which makes sense because it's just a VW with nicer interior. Mine happens to also have a nicer unibody. If I weren't so enamored of Aluminum cars, I would probably have just bought a Nissan. They are easy to work on and their documentation is absolutely top-notch. Maybe supercharge a first-gen, lightest-weight 350Z. Or perhaps another Subaru. Sure the heads go wrong sometimes, but they're cheap and they're easy to work on if you stick with the four cylinder. I had a 1993 Impreza LS and I probably should have kept it, but it may have saved a life which is an unrelated tale.