It pretty much nullifies this concept, at least from pro reviewers. When a reviewer states that an expensive cable has a harsh top end, and they prefer something else, that disproves the placebo effect .
Actually, it doesn't disprove the placebo effect, or expectation bias, at all. It could just mean that that reviewer has a different set of expectations. Maybe the reviewer actually has a bias
against expensive cables, as many folks seem to do. That could skew the results just as much as having a bias in favor of expensive cables.
That double-blind test you cited was pretty interesting. The fact that the results were so exactly split is is particularly intriguing. It's always good to have some actual data. I don't think it's the last word, however, nor am I saying you suggested that.
One way in which the study could have been better, I think, is that as far as I can see, the players all
knew that there was supposed to be a change in gear when they flipped the switch. They didn't know which position was which, but they did know that one position was one thing and the other position was the other thing. The fact that they knew that the two positions involved different hardware is a
possible source of bias, in that it could encourage people to believe there was supposed to be an audible difference when they actually didn't hear one. The fact that the preferences were so evenly split would be consistent with this possibility, though it does not prove it by any means.
An even better test--and I admit I'm not entirely sure how it would best be rigged up--would be to set up a situation where in some cases
nothing changed when the switch was flipped. If the player still hears a difference in that situation, you know that expectation bias is at work. This possibility wasn't sufficiently ruled out in the study.
Another improvement would have been for the players not to have known when or in what direction the switch was being moved. I'm not sure how that would have best been done either, but it would have helped rule out the possibility of expecting a tone change when the switch was flipped.
In any case, a test of this sort generally provides more useful data than subjective nonblinded comparisons.