Why power cable effect overall syste sound?

Knownothing, First of all I would like to say I have never said power cables don't make a difference. I have tried numerous power cords and I hear the difference in each and every power cord as I do with every speaker wire and interconnect. System resolution would have to be at an all time low not to hear the difference. What I am saying is I prefer the sound of the original power cord. Maybe I have a purist attitude in this respect and obviously I am not alone. If a given system does not sound right I simply look elsewhere.
I have tried after market power cords on all types of equipment. I was only using amplifiers as an example because of the extreme differences in the power cords of the two amplifiers I mentioned and to make my point.
I understand this thread began with "Why power cables effect system sound", but it evolved rather quickly.
Power cords are not the only thing up for debate these days. I recently spoke with two well known amplifier and preamp designer/manufacturers in a discussion about speaker wire and interconnects. Both said they did not take speaker wire that seriously and they felt the interconnect was much more important. Personally I have had a change in speaker wire make or break a system. However, I respected their opinion and it gave me something to think about when one of them said the most important thing for speaker wire is that it is efficient since it is tranfering the power.
In this hobby there is no right or wrong and there is no such thing as a perfect system. What we believe today we may find out is wrong tomorrow. The main thing is that we enjoy the music along the way. Isn't that how we got into this in the first place?

Hifitime, As I mentioned in a previous post, the IEC socket creates another questionable connection. This is why I prefer a hard wired power cord.
The manufacturers are under a terrific amount of pressure by reviewers and dealers to make changes in their products and it is not always for the better.
I recently commented on a post regarding the well respected Dunlavy SC IV speaker system. John Dunlavy did not believe in spikes or cones and he did not believe in bi-wiring his speakers. However, the reviewers and dealers pressured him until he finally gave in and installed bi-wire posts on his speakers. I tried my SC IVs both ways and the speakers were more coherent with single wire with no loss in dynamics.

A few years ago or so on another forum a member who had an incredible listening room constructed (~$75K) and easily over $150K of gear swore up and down changing power cables to his powered sub inside the overall speaker enclosure made a noticeable difference in sound. People gave him the usual "no way" for the usual (correct) reasons. He finally did allow some of the other members to come over and do a blind test. Somehow when somebody else touched the power cables they lost their magical powers - he could no longer hear the difference when he didn't know which cables were being used. Funny how what you remember may not be what you actually heard in the first place even though you'd bet money on it.

I would suggest that the real question that should be addressed is not whether aftermarket power cords can make a difference relative to stock power cords (Grant has provided plausible, and in my view, valid explanations for that), but the reasons, if any, that very expensive upgraded power cords may provide additional benefit relative to less expensive upgraded power cords.

Grant, I'd be interested in your take on that. Most of the advocacy for upgraded power cords tends to deal with the question of whether and why upgraded power cords will perform better than stock power cords. But what are the reasons that say a $2000 power cord might perform better than a $200 power cord, the $200 power cord presumably providing the shielding and other factors you and others tend to cite as rationale for upgrading.

Obviously the $2000 power cord will utilize more expensive materials and/or construction techniques than the $200 cord, but how and why does that translate into better sound?

Regards,
-- Al

Or better yet - Show the difference.