I.D.C.:The music you listen to will probably have been created in a recording studio. Even if it hasn't -- it's a live performance perhaps -- by definition it will have been recorded using electrical equipment of some sort. This equipment will have been mains powered. Now, I've spent time in recording studios, and I can't say that I ever saw one that used `audiophile mains cable' to power its mixing and amplification equipment. In fact, I've seen mains leads scavenged from kettles and toasters to power the mixing desk. As a matter of principle, your sound reproduction can never be any more accurate than the original recording. So if you spend more on your cables (mains or otherwise) than the studio does, you're wasting your money.
This is not proof that mains cables do not work. So the studio the author used to spend time in didn't use good mains products...but how good was this recording studio. Some recordings (even on main stream albums) are rubbish, and even if it was a good recording, who's to say that it wouldn't have been better with good mains products.
Besides, just because he didn't see good mains products doesn't mean that they were not there. If this is a recording studio then there is a good chance that an electrician has already ensured that the mains is clean in the room to start with (yes they can do that, by using filters and / or having separate mains supplies). Fair enough, they may have used basic kettle leads, but the mains may have already been cleaned before this point.
Think proof of concept: If one system was plugged into a room which had terrible noise running through the mains to the extent of causing a hum through yuor speakers and an identical system with very clean mains products you will notice an enormous difference. Every thing else is just shades of grey between these two extremes.