1439bhr- I think the answer to your question is that from the manufacturer's point of view, people probably won't pay more for the product if it has a better AC cable, and therefore anything they spend on upgrading the AC cable comes out of their profit. Even though high end units don't typically have large model runs, if the company is pushing out 10,000 units over the model life, that might be $10,000-20,000 over the model run. And most manufacturers have several models going at once, so to them it adds up, if there is no benefit in terms of increased income.
The fallacy of ac treatment
I see a lot of threads related to managing and tweaking the ac powerout end of electronic systems. Much has been said about dedicated wiring, termination and even the right kind of extension cords to use. I work for an electric utility; and that's the extent of my credibilty here. The majority of you will no doubt be far more erudite wrt music hardware. Just a thought, though: domestic ac distribution goes thus: power station-step up-city-step down-subdivision-final step down. As far as the utility is concerned, you and all your neigbours are collectively the load for the step down tranformer. Any inductance/capacitance created by your neigbour running motors/tubelights, etc is felt by the lot of you. Additionally, the voltage frequency will almost always move around a tolerance from 50hz as the whole country turns on the air, off the lights - changes all the time as peaker plants ramp up etc. Nothing can change that- the frequency of the grid supplying your city is the frequency in the mains at your house. So what's my point? Well only that how much difference can the last 10 feet of cabling, etc make when the other hundreds of miles are outside of your control? And more importantly, frequency is one of the most imp parameters for measuring electricity quality (your expensive hand-coiled toroids are entirely subject to the f in the primaries) and nothing other than running an f generator can shield you from that. Methinks all the improvements you see from ac cord treatments are pyschosomatic. But that's cool.