Jchen--Your understanding of the placebo effect, at least as it applies to perception, is wrong. (It's actually wrong even as it applies to medicine--the placebo effect can work even when the doctor tells you the pill won't work.) Simply knowing that two cables are different can make them sound different to you. In studies of hearing perception, people who listen to the same thing report that it sounds different about half the time.
That doesn't mean that all cables sound the same. It just means that when they do sound different, it might be real, or it might be in your mind, and there's no way to know for sure--short of the sort of objective scientific test that will be pooh-poohed here, so let's not even get into that.
Now, you're free to say, "I don't think it's in my mind," and buy whatever cables sound best to you. Just don't fall into the trap of thinking you have to denigrate science to justify that. Nobody has to justify anything in this hobby.