chemman,
I think that bias may occur, although I am not sure it is always in favorable direction.
For whatever it is worth, I recently blasphemously bought a cable (RCA) without ever listening to it. It was a few-hundred-Dollar "upgrade" from $15-16 cable I had had (and still keep). I bought it for the looks. It simply appeared "fancier" on the pictures and was affordable enough for the purpose I had for it. I did not expect much and I got exactly that. The sound is not better for sure. In fact, I think nothing changed although someone might convince me it is even a little worse. I kept it connected because I like those shinier connectors, which I actually almost never see as they are behind the equipment. Was it worth it for the sound? Not at all. Was it worth it for me? Definitely yes. Would I buy it again? No way, novelty has worn off.
I suspect that some, probably not all, of the buyers fall in the similar category. They want finishing touches to their equipment, a final stroke they may feel is missing. Something that, at least in their minds, matches the rest of their system. It does take some sheepish courage to admit you fell for the looks and that is where some of the bias may come from.
If I have to use another RCA cable, I will go back to the $15-16 pair. Unlike these more expensive ones, cheap ones are pliable, have angled connectors, and can easily fit behind the equipment. Expensive ones are hard to bend and fit anywhere without strain. Does anyone else have a problem with stiffer cables?
To answer the title question of this thread, yes, cables matter, but it is not always for the sound.