Without wishing to offend, I don't really care what you think of the argument. I'm more interested in what legions of psychologists and behavioral scientists say on about the matter. If you bothered to read about the subject rather than try to defend the indefensible maybe you would understand the thinking behind the methodology.
The problem with this is, and quite clearly also suited to other instances, psychological observation will not take into consideration the cables themselves, but assume and work with the psychological problems posed with the opinion of the belief system itself.
For instance why did you buy an amplifier?
Because I wanted it, it was an upgrade over the one I had.
And what made you feel you had to purchase another amplifier?
If the psychologist was into stereo equipment himself, would the opinion be different, or different methods used and any sort of sensible conclusion met? The investigation in itself is usually flawed due to the nature of the investigation itself. He believes there is a difference, infering it is him who believes not others, he feels compelled to spend more on another purchase of what he already has, infering no reason for the purchase.