There have been several times in my audio journey when I listened to a system that was beyond my ability to fully process it. Over time and with experience, our brain fine tunes itself to discern the differences in fidelity.
The differences I hear in my system to a non audiophile might be difficult for them to hear. When I point things out, sometimes they can hear it, sometimes not.
So perhaps the law of diminishing returns also plays into not yet having the developed palate to hear the full differences.
I think what he's saying is that the sonic differences are subtle.
To the average person on the street spending $5,000 dollars on a stereo is quite extravagant. To spend 10x or even 100x that amount is nearly incomprehensible. I will never say that you can't get better sound by spending more money, nor do I begrudge anybody so inclined. I just think the concept of accelerated returns in audio reproduction is false. I find it interesting that nobody has offered actual examples of it happening.