The entire exercise is predicated on the notion that if a person consciously listens to an audio recording for a while they will be able to provide a completely accurate estimation of the quality of the recording. To some degree that is true, but I dispute the idea that it is completely true.
Yes, there are crazy audiophiles who will tell you that special crystal bullshit gives them a better sound, nevertheless there is an element of truth in a degree of audio fidelity than is immediately and consciously apparent upon a single casual listen. Sometimes it can take listening to a given recording a few times before you start to appreciate all of the nuances. Maybe you don't notice the little things like the squeak of the bass drum pedal the first few times you hear it, or the richness of the intonation of the clarinet. Or maybe you don't immediately notice that the cymbal crashes are all fuzzed out to hell and back by compression artifacts because you weren't paying close enough attention the first time you listened, but on the 10th listen it starts to become a real annoyance and you start to think seriously about acquire a better recording or encoding.
Here's a perfect example. Pink has a very popular song called Raise Your Glass, you can listen to it on youtube here: http://www.youtube.com/watch?v=XjVNlG5cZyQ. In that song there are many prominent and annoying high-pitched beeps (right in the middle of the chorus even), but I find that most people do not even know they are there, they do not consciously hear them, their brain just filters it out. But once you pick up on it, they become obvious, you can't help but hear them. And the same is true of things like encoding distortion. If you draw the bar at exactly the boundary where people will be able to consciously perceive a difference in quality based on a single listen then you will have placed the bar too low. People will have a slightly lower appreciation for the recordings due to factors they may not even consciously be aware of.