But maybe all these reviews and downloads came after getting featured by Apple. I surely believe that your App will be downloaded a lot more times if you are highlighted by Apple and being highlighted by Apple could mean to people "that the App is definitive worth it and good" and so they probably more likely to give good ratings.
I'm sure there was some spike in downloads because of the feature, however, it wouldn't be more than a few thousand. This isn't very significant considering that Halftone probably has over 100K downloads (extrapolating from the assumption that 1% of downloaders submit a review). Of course this is a very rough estimation, but I think it puts Halftone's traction into perspective.
I don't know just my 2 cents.