I apologise for derailing the thread a bit. I just find it frustrating that the barriers to entry are so high these days, and its exasperated by these really premium brands. The purpose of these very premium brands does not seem to be just about the piano itself, you never see these brands on stage for example. I think these pianos are better compared to a piece of high end furniture than a musical instrument, because the only musicians that can afford them will be very wealthy ones. Its a display piece for the discerning buyer as Joseph Fleetwood said.
I think you have mischaracterized what Mr. Fleetwood said as a whole. It seems like you just have a lot of anger about something you have not yet tried, and an industry you simply don't know much about. The "price of entry" for pianos has continued to go down, with inexpensive digital pianos simply taking the place of the entry level spinets of before. The premium pianos are useful to those who:
1. want to buy on the "prestige/exclusivity factor"
2. intermediate level players who appreciate the differences in touch/tone/appearance vs. cheaper pianos
3. advanced/professional level players who use the full capabilities of the piano as a tool to express themselves artistically
For some reason, you seem to lump everyone that has one of these pianos in category #1. And unlike other objects referred to in this thread, a high-end piano takes several months to a year to produce just one finished example. Even the Japanese makers you cite all produce a high-end line (that is made much more slowly with a lot more hand labor and more expensive materials), which are priced just as high as many European-made equivalents.
Then I worry, having now been learning to play myself as a middle aged adult, that when kids want to learn to play the opportunity won't be there for most of them like it wasn't for me as a child. If a normal working class parent goes online to look at piano costs they are going to be put off and feel like they can't give that opportunity to their child. Its a real shame. And what happens then is you look at cheap pianos on ebay or whatever, and they are brands you've never heard of and can't find any information on, or they are only small ones (<110cm) when all the advice online says bigger is better etc etc. So you end up between a rock and a hard place.
Life is a series of choices. Some of the forum posters you have attacked, value having a fine piano more than a $1,200 phone or a $50,000 SUV, or needing to buy insanely marked up alcohol when we go to a restaurant. Some of us own a fine piano on a middle class income, and we just make financial choices to make it work. At all points in my adult life as a working pianist and music teacher, my pianos have been worth more than my vehicles by 100% or more.
I don't think spending $5,000 on a piano for a beginner or intermediate player is a bad investment, considering it will last for decades with decent care and maintenance. It costs far more annually to give a child lessons.
p.s. information about just about most brands of pianos you've never heard of can be found at pianobuyer.com and I don't advise buying a piano via (or using as a robust pricing reference) eBay.