Coming from a 240V 50hz country Ive also wondered about this. Not so much the voltage but the line frequency. Aside from the supposed better shielding and rejection of after market powercords, Ive heard more than once about these being tuned in materials and length for electrical 'resonances'.
If this has any truth, and the 'tunings' are frequency dependent then surely a cable built for 60hz will not benefit from this aspect when used with 50hz?
Food for thought.