You can definitely take characters like Teal'c and Teyla and Ronon somewhere else... but it takes more work. Your average white female writer from the US or UK or wherever has to go outside her cultural 'comfort zone' in a way I think has more to do with the characters 'outsiderness' than the fact that they were cast as colored people.

So for me, at least, the question isn't 'why don't people write more about Teyla or Teal'c or Ronon', but instead something like 'if Lorne was black, would people still write as much about him as they do'.