I am not sure being a "real musician" helps in the this case, although I can speak with some authority on my own instrument. In the case of the piano, the expense of a �100000 concert grand comes about because they are expensive to make. They take a long time to be made by hand, and if you visit the factory and see it being done (as I have) you have the feeling that they aren't such bad value (especially compared to say a luxury car which is machine made and will only depreciate and stop working in the end).
On the materials question: Fazioli in Italy, a company born only some 20 years ago, have done a lot of scientific research into why pianos sound how they do, and make theirs according to the principles they have deduced. They are fine instruments but they have their problems, and I don't like most of them. And they are as expensive as Steinways and Bösendorfers, so they haven't shown up those two as a scam.
There have been many small technical changes to the piano's action, particularly in recent years. Many of these are resisted by pianists because they simply don't help. It wouldn't help us to spend �1000 more on "snake oil" in the sense of special modifications, because no-one can see them, and if they don't improve matters then they will simply not be acceptable. The invisibility of the piano's internals helps in that respect.
There is one possible exception to this and that is Fabbrini, who are a Steinway dealer in Italy. The original owner was Michelangeli's technician and he and his company have supplied instruments to people like Pollini, Schiff and many others since then. Pollini ships one all the way to NY for his Carnegie Hall recitals, for example. No-one really knows what the difference is: whether they are actually materially modified or if they are simply very well prepared (i.e. adjusted), and it doesn't really matter because if the pianist wants one they usually know why and it doesn't matter what anyone else thinks.
It helps that this is a single case: there are not loads of people sprinkling magic dust on pianos in this way.
As for violins, the price of old Italian violins is because they are severely limited in quantity, and are definitely special - and that specialness is something which is more and more understood, and therefore can be replicated to some degree. Stradivarii's prices are the highest because of the name, but there are a lot of hugely expensive instruments by other people.
It is also worth noting that newly built and recent modern violins for classical soloists (often using the understanding of why the old Italian ones are so good) can be expensive as well (well over �100000). I know quite a few people with �100000 string instruments. All high level professionals would simply have to have something costing that much, otherwise they would not sound the same.
...I had a long-term girlfriend some years ago whose violin was worth �150000. (Her parents had bought it for her when she was 13 and won a major competition.) I used to pay her insurance premiums, so I know.

What's interesting is that there probably *is* some effect of the material used on the sound of the saxophone (though, as pointed out in the article, the size and shape of the bore is of the 1st order of importance). Unfortunately, all this marketing rubbish ruins any possibility of discovering the truth.
I have no doubt that's true - but I don't know how much it is with saxes.
I just played with Melbourne Symphony and instead of a contrabassoon they had a
contraforte. I believe it is not wood but some sort of composite. The website doesn't explain but I saw one and discussed it with the people there. It sounded incredible, I have to say, though I don't know how much the material is part of that.
One more point: the difference between instruments is NOT defined only by raw sound. It is a lot to do with what (musically) it allows the player to achieve. That can't easily be measured, and can easily be misunderstood. But it has to be accepted that players would not tie up their whole life's earnings with a loan for an expensive instrument unless they thought it was worth it musically. It is not a luxury item.
Excuse the rambling. I hope it has provided an interesting perspective.