Well, there's certainly two layers there, in that all the coloured people in Stargate either start off as outsiders (Teal'c, Teyla, Ronon) or become outsiders (Ford). So part of it is certainly attributable to the way the characters are written on the show.

However, I personally feel that the argument of "they're just [insert differentiation here]" breaks down when we're talking about work derivative from the original canon - whether authorised (tie-in novels) or unauthorised (fanfic).

I mean, when people go on about how the like fanfiction because of the "ability to take the characters somewhere else", it would surely stand to reason that the characters least "taken somewhere else" would be the most attractive prospects, right?

Or am I not thinking in the appropriate herd-mentality? :)