Minor: Distributions of ratings are not usually normal about the average possible rating -- they are usually skewed to the positive end, because people are pretty good at selecting what they read or view. The solution presented will tend to skew low-frequency ratings too far toward the average. It should be easy to calculate an expected average for your site, and use this instead of 1/2 for the formula given in the post.
Major: What you really need is a missing data point: the number of readers who haven't made any rating at all. It's pretty clear if you think of two examples:
Item 1 1,000,000 views 10 positive ratings 1 negative rating
Item 2 15 views 10 positive ratings 1 negative rating
Clearly, readers feel pretty blah about Item 1. You're much better off displaying Item 2, other things being equal, but the formula doesn't distinguish the two cases.