One thing I noticed is a regional bias. I did some comparisons using this site to help prove that this area needs more good courses. I moved from Charlotte 15 months ago so I used that area.
Around here (north and NW of Chicago) are a whole bunch of open, short, boring 9-holes and a few mediocre 18 holers. I averaged out the ratings for both areas and was amazed that they are almost the same (about half a disc different).
The lower end of the 18-holers in Charlotte (Boyd Hill, Kilborne, Reedy Creek and Sugaw) absolutely blow away the 18 holers here (Bevier and Fairfield). And, Charlotte has epic courses like Hornet's Nest, Renny and Winthrop.
I know this is just one isolated example, but I am willing to bet a lot that this sort of issue is all over the place. Since the number of well travelled reviewers is much less than local players/reviwers this sort of bias will not go away I doubt.