Mmccoy, that's a fair question, but one that's been answered in detail a number of times. To save you a bit of research, the short answer is, and please understand this comes from a non-techie, the differences lay in the shield configuration, conductor size and construction, quality and types of materials and workmanship, and, in some cases the additional components (i.e., filter materials, also called "magic dust"). None of that is to say I personally buy into the mega-price cable story, BUT I also do not have first hand experience with extremely expensive power cords. Certain of the claims do, on the surface, make sense. My ears say upgraded cables do make a difference, though. My only question is where does the "improvement curve" drop off into silliness, if it actually does? Hope that's helpful on some level.
BTW, if any of that is grossly erroneous, guys, please correct it. I try to pay attention, but don't always get it right.