Like the Emperor's New Clothes, many people let themselves be conned into believing that a higher truth exists, even if they cannot hear it. There is no disputing that hearing can be improved with practice and that you can learn to recognize detail, but that is certainly not the same as imagining something that doesn't exist to begin with. And, logically speaking, just because a large number of people believe something does not alone make it the truth. Even more important, all the audiophile tweaks in the world are meaningless compared to such basics as installing proper acoustic treatment in the control room and using solid engineering techniques.
It is difficult to prove or disprove issues like those I have presented here because human auditory perception is so fragile and our memory is so short. With A/B testing - where you switch between one version of a signal and another to audition the difference - it is mandatory that the switch be performed very quickly. If it takes you fifteen minutes to hook up a replacement amplifier, it will be very hard to tell if there truly was a difference, compared to being able to switch between the two amps in less than a second. Even when switching quickly, it is important that both amplifiers be set to exactly the same volume level.
When all else is equal, people will generally pick the brighter (or just louder) version as sounding better, unless of course the sound already was too loud or bright. People will sometimes report a difference even in an "A/A" test, where nothing at all has changed! And just because something sounds "better," it is not necessarily higher fidelity. Goosing the treble and bass or adding a little compression often makes a track sound better, but that doesn't mean the result is more faithful to the original source material.
Psychological factors like expectation and fatigue also play an important part in one's assessment of sound, even when nothing physical has changed. If I brag to someone about how great my studio's playback system sounds and then that person comes over to hear it, my system always sounds worse to me while we're both listening. Finally, it's important to consider the source of any claim, though someone's financial interest in a product doesn't mean the claims are exaggerated or untrue either. But there's probably more than a little truth to the popular sentiment, "The most important person in a company that makes audiophile speaker wire is the head of marketing."