I think this topic gets misinterpreted alot based on incorrect assumptions. Its not that out of the box, all amps sound the same. But, an amp that functions within a normal range (doesn't have obvious deficiencies, like 20% distortion, for example) can be made to sound identical under test conditions with another amp via corrections. So, with that said, this is more to rebuke claims such as class A or tube amps' 'warm' sound. Not many true class A amps out there. Why? They are horribly inefficient, drawing almost full current with no sound output. Many amps claim class A, but I'm willing to bet the vast majority of those are class a/b that operate in class A up to a fraction of a watt or so. Tube amps? Warm sound likely caused by frequency response bump and distortion, both of which can be duplicated by a solid state amp.
I think the point is to try and dispel the myth that certain components and technologies automatically offer better audible SQ, like clearer highs, better sound stage, tighter bass, etc. Some technologies might offer better measured statistics, but the question is, is it audible? 0.1% distortion vs 0.0001% distortion will sound the same to the human ear. Technically, 0.0001% is a lot 'cleaner', but its way past the threshold of audibility. So, the point is, don't buy an 'sq' amp thinking it will be 'cleaner' sounding than your current amp. There are many reasons to buy a high end amp over an entry level one, but 'sq' is not one of them.