Hello Metro04 - well, I thought the "miles of wire" myth had been thoroughly debunked, but I see that it lives on.
There are no "miles" of anything in the power grid - it is a series of interconnected systems and structures (generating stations, transmission grids, substations, distribution grids, distribution busses, regulator banks, taps, stepdown transformers, meters, distribution panels, and then finally the wiring contained in your home). The electrical energy transmitted through these systems undergoes frequent changes in voltage and regulation. There are dozens, even hundreds of connections, each of which constitutes a separate circuit, not one long continuous circuit. Thinking of these interconnected systems as some sort of long link as you have suggested is just plain wrong. Looking at it that way is like looking at the telephone communications network as a long wire between you and the phone company, which is equally wrong.
"Audiophile" power cords can indeed affect the performance and sound of gear, but not because they have an effect on what happens back at the power generation station or in the transmission grid. Contrary to the notions of some audiophiles, most of the noise found in household electrical systems and radiated into the environment as RFI/EMI is generated in the house, by household equipment, not back at the power plant or on the transmission grid.
Don't think of a power cord as the "final 3-6 feet," because it's not. There is a connection made at the wall outlet, not a contiguous link, which means that the power cord and the wiring in your walls ARE NOT THE SAME.
Since the bulk of noise and radiated energy are generated in your house, that 3-6 ft of connection from your gear to the wall outlet or powerbar can make a difference. A power cord that rejects RFI/EMI, whether in the household electrical system or radiated, can noticeably improve the sound of a resolving audio system.
Not all "audiophile" cords can do this - some have no effect, some can make things worse. Interaction with the equipments' power supplies can have an effect as well - positive or negative. Not all gear can show the difference between power cords. But claiming that all power cords that attempt to ameliorate the effects of noise are "snake oil" is dogmatic and incorrect.