Admittedly not being a physics degree holder, I've still got to admit that my tendency is to agree with Gunther and Blue Bear. It really sounds like a load of crap, and even if there was a kernel of truth to it, it would be so negligeable as to make spending 5x per foot of cable extremely cost inefficient, especially compared to throwing that extra money at other acoustic problems.
Next time someone has a chance to talk to Bob Ludwig (or someone else at that level) who basically spends all his time (when not actually mastering) critically A-B'ing every conceivable aspect of the listening chain... it would be great to ask him what he thought of this whole issue. I'd be far more likely to take his word on the issue than a 20 year old GC salesman with no technical background (no insult intended).
I usually bump into him once a year, but it's usually in November, unfortunately.