That link's right. Oxygen-free isn't a big deal, but is one of those things which must be listed for enthusiasts to take a product seriously.

The snake oil salesmen will have you believe that copper oxide crystals can function as rectifier diodes. Since audio signals are alternating current, the last thing you want is for that signal to be converted to DC. Good thing they're full of crap.

Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs
-Chris