If you do an amazing job, and I pay you an amazing amount. That amazing amount could vary depending on your cost of living.
I agree in a perfect world that you should get paid the same no matter where you are, and globalisation will probably head in that direction. But so will cost of living balancing out too (if people in lower cost of living countries are earning lots more money, the price of things will go up.... supply/demand).
I guess ultimately, when comparing what you pay people, why use the dollar amount as opposed to the benefit to their lives. Shouldn't you be paying everyone an amount that equally benefits them? Why should one person be far greater benefited from their salary? Ultimately it's what you do with the money that matters, not the number on the note.