In a nutshell, with bitcoin being the medium of payment the location of a writer in USA won't be enough reason to earn higher than another writer in Africa.
that would work in a world where everything is equal. The point is that a freelancer in africa would be happy with for example 1000 usd for a month of work, and someone in the usa or europe would not do anything for that amount of money, bacause it wont be enough to make a living. And freelancers will compete on price. Years ago we had a job posted on some freelance site. First an offer of 3k from the usa, than 1.5k from GB, and then more and more offers from india, ending @ 400 or something.