I figure several people will rip apart whatever I write, but I'll give it a try anyway. Then I'll go do something else while people figure out what's wrong with it.
No lab coats were involved.
Cable testing is a big pain in the butt to do. You have to have someone swap out cables while you wait (with your eyes closed). The person doing the swapping has to be really good at the whole thing to be both quick and accurate (like not accidentally get something out of phase). The fact that there are sometimes differences in how loud things are is problematic. Do you compensate by turning down the volume, or not? Good reasons against both.
If the attitude of the listener is important, then I'll include mine: I was really wishing the whole thing weren't necessary, but I did my job, the same way I evaluated the other stuff that had to be listened to. There are many expensive things, by the way, that I was very unimpressed with. I felt resentful that we had to give so much attention to magic boxes that the press was touting, when they were in. We had a clutter of Mitch Cotter's blue boxes lying around on the shelves for years as a result of one of those enthusiasms. When fancy cables came into fashion, I figured it was more of the same. In some cases it was, and in some it wasn't.
This probably won't sound like scientific methodology the way I'm writing it, but the routines got established well enough that we were doing good evaluations. I mean, we didn't do things we didn't need to but did everything that was necessary to prevent contaminating our evaluations. The people listening couldn't see what was changed. We only changed one parameter at a time. We avoided discussion that would give away what was going on. Most of it was just quiet, businesslike, and very very tedious.
My results were consistent with those of others when they got to be the earsand have me do the switching. I certainly heard things I was not expecting to hear, and some times I heard things I definitely did not want to hear - such as when a customer brought in some new preamp that was (gasp) better than what we had to offer in the same price range!
So picture a person, eyes closed, in the comfy listening chair, and a very revealing setup, listening to I'm Your Man by Leonard Cohen. The listener knows the CD well, and recalls that there's a kind of throaty growl going on in one of the tracks, and hears it as usual. Then a change is made, and suddenly there is clarity that makes the blurry sound a lot less blurry. There is new clarity, plain and simple. Oh, crap, the listener thinks. Now I have to pay attention to cables.