Actually it has to do with cleaning up the pops, crackles, RF, and digital noise that comes from any industrial use on your grid and the noises picked up from your household circuit. The last six feet of line before the power goes into the amp actually attracts the "noise" and shunts it off to ground (simplisticly speaking it's acting as a filter), the power is then much cleaner which keeps the amp from amplifying a noise threshold that you can't typically hear until you take it away, then you notice the difference of a much blacker background that makes things much sharper and clearer, the detail and definition are improved dramatically.
I was a nuclear missile technician in the military so I have plenty of background knowledge that causes me to say bull as well, I know that the power supply should negate this noise as should the current reserve capacitance. When I told Dave Belles who designs amplifiers he had to hear the power cords on his amps he told me a power cord shouldn't make any difference, but he was willing to listen to a couple of different ones JPS sent to him and loves them. When he is tuning a new design for it's sound character he uses them because he can hear so much more detail but then he has to put the stock cord on to make sure it's allright with that.
The great bang for the buck on the amplifier comes with the $500 cord, it makes quite a difference, then the $1500 is enough better that it seems to make that $500 cord seem to do about 15 to 20% of what it does which makes it seem even more in perspective for the price, then the $3500 cord is even smoother but gives a little less bang for the extra money than does the one before it. In a super high resolution system if you have one weak link anywhere it can make the system sound hard and edgy, the Aluminata can tame a huge degree of that edginess which is why it seems so to be so much worth the money. A lot of people find their mega-buck systems to be too hard edged to enjoy and cable can make huge difference in that respect.
I would have about a $10,000 system if I weren't selling this stuff, but I have to keep all of my manufacturers equipment on hand for people to hear. I definitely have my favorites which are not necessarily the most expensive models, I can set up a $70k system but the one I seem to like best is about $35k and uses a $3500 Belles 350A amp over other amps I have that are almost $20k a pair. I also tend to show what I feel is the better product even if the person is interested in the more expensive models.
I had three aerospace engineers over a few months back that came in loaded for bear with all their pompery about the hundreds of thousands worth of test equipment they had at work and how lampcord is as good as any cable costing thousands of dollars etc. They wouldn't buy what they were hearing until they heard it again in their own systems so I had to loan them quite an array of wire but they all bought different grades of wire according to what they could afford. They're still trying to figure out how wire can make any difference let alone how much it does. They had Levinson and McCormack caliber gear with Monster wire so they are pretty thrilled with the improvements they got.