The original question still stands: What do insanely wealthy people buy, that ordinary people know nothing about?
By the definition of the question I can't know the answer myself: I am "ordinary people" so I must know nothing about it. So what's left to me is to suggest parallels at the level I do know something about.
Another example of a "middle class thing", not related to things or appliances: services, in particular moving. I changed flats many times in my life, more than 10. I used to pack, load, unload and unpack everything by myself and at some point it started to take 2-3 days of my time full time. Then one time I contracted an end2end moving service (you just give them the keys) and I would never ever go back.
Recently a friend of mine was moving and asked to help to load the truck. After an hour of sweating I asked why he didn't contract someone -- this idea just never crossed his mind. A year later he was moving again and was grateful for the advice.
Surely, rich people enjoy services that would never cross my middle class mind? A governour for the child maybe? Well I would never know.
That's very much country dependent. I live in a country where anyone middle class has a house keeper either from Phillipine or Indonesia (cost about 10-15k usd a year if you're not an asshole and don't pay the lowest possible salary). That housekeeper's work is to take care of the children and do the housework. Upper middle class people have two. Then the next level up is to also have a private driver.
Governor/Governess is after that, I know two people who do it, they hired someone directly from UK for about 45k usd a year. That person takes care of their child and helps with education/homework etc.. Main advantage compared to the housekeeper is that the governor is more educated and so will be able to actually teach things to the child. But it's not necessarily super common and I know plenty of rich parents who decided not to do that and instead invest more heavily on tuition/activities and later (starting from 9-10 years old) summer camps at Oxford, Cambridge, John Hopkins, etc...
Nowadays, the trend is that people buy the cabinet frames from Ikea, and then buy the doors, handles, and bottom support from someone else who makes more durable ones.
The thing is that with Ikea, I kind of know what I get. From a custom kitchen cabinet maker, I could get something that lasts a lifetime, or something that wears quickly.