It's definitely an interesting concept. I've never thought of looking at that. I don't think that I would trust a reviewer any less solely based upon them having a limited course territory, though. I might start looking at maps for fun, though.
I definitely look at pictures and mostly trusted reviewer reviews when selecting courses to play. Although proximity to my route and destination probably play the biggest role, sadly.
Using your territory concept, I've never played a big Colorado mountain type course. I've played a desert course, but it was on a man-made desert are, and not really a natural desert/wilderness course.
Otherwise, I've played 78 courses. That's not a huge number, by any means. But I have gotten to play a pretty wide variety of courses with a couple obvious exceptions noted above. So I feel that I have a pretty fair concept of courses to be able to give a useful, objective opinion.
Now, pros would have to adjust their expectations of a course based upon the limitations of my game. For example, I try to always mention by consistent driving distance as a point of reference. But a thumber/tomahawk or forehand player could definitely look at a course differently than I do based upon the limitations of my game.
But that's kind of the point of having multiple reviews. Different perspectives definitely prove useful.