Last night at a New Year's Eve party had the unfortunate "good artists can come from anywhere" argument. Since the person espousing that was too passionate or stubborn to listen, here's the counternarrative:
An artist can be outside a major metro area and be discovered in the near or long term. But if art is dependent on the person as well as the moment, as Matthew Arnold observed, then it stands to reason that the moment will be found (or accelerated) where there is the largest concentration of people who can make it happen. Given how many obstacles an artist faces, why would you handicap yourself being outside that zone if you had an ounce of choice in the matter?
Part of the chemistry of the moment is a shared professional language. Again, an artist doesn't have to speak that language or self-identify with the community that speaks it, but why would the artist choose a mute or deficient community if he or she had any choice?
Afterthought: the Internet helps the geographical hurdles somewhat, but at the end of the day, a painter, say, is not going to be evaluated based on jpegs. Someone is going to have to verify the work--why not the largest possible number of someones?