Nothing about his analysis is limited to local reviews -- the mean is a limited measure regardless, and the limitation of reviewers reviewing at different times

Nothing about his analysis is limited to local reviews -- the mean is a limited measure regardless, and the limitation of reviewers reviewing at different times is a function of the number of reviews per unit time, not locality. (They're correlated, obviously, but far enough out in the "long tail", even international reviews are going to be thin.)