I have more than 20 apps on the appstore. None of my apps have more than 20 reviews, so I cannot judge these numbers. This might be true for 99 cents app, but I am not sure how directly correlated will this be for >$4.99 apps.
I checked a couple for $4.99 and the numbers are below 200 except a couple whose numbers are close to 300
so the theory seems to be working as long as you are don't count your own or your friend reviews.