I read an article in the Stereophile archives
http://www.stereophile.com/content/carver-challenge about Bob Carver voicing one of his consumer amplifiers to sound exactly like a much more expensive, and well regarded amplifier (CJ Premier Four). The Double blind testing produced two identical amplifiers, indistinguishable from each other in every way.
The point is, just because AB testing doesn't result in a clear winner, it doesn't mean (to me) that the products are the same, quality or otherwise. Modifications such as cabling may take a great many hours to identify the changes they've made in a system. I'll readily admit that I've not been inclined to spend the time to evaluate the effects of power cables in my system, but I do have an open mind about these things. However, I have, up to this point, relied only on my basic knowledge of electricity to make decisions like these.
Note: Speaker cables are on my list as a near future purchase, and I'm going to rely on the recommendation of another member (Tim) in another thread to make my first choice in this crowded marketplace.
Note two: That open mind I spoke of really needs (I think) to work both ways as far as cost/result of any upgrades; Return on Investment. Far too often (I think), I am asked to have blind faith in the design and efficacy of a hugely expensive product, while being told that an amplifier/source/loudspeaker is Mid-Fi/No Good because it is brand X and we don't like brand X and brand X is Low Quality and No, I haven't heard or seen this particular brand X model because I don't need to hear it because I already know what I think of it because it's made by brand X, etc....
(Is that a rambling sentence, or what?)
Just my 5 Cents (we no longer use pennies in Canada, so I've rounded up. That's the kind of good value I offer!)