The initial AppStore rating system allowed anyone to review the apps without purchasing which flooded the appstore with some stupid reviews by foolish people (no offense!).
Awhile back, Apple introduced the new review system that allowed only the buyers to review an app in an effort to get the situation under control. While the issue of stupid and foolish reviews was solved (for the most part) the original reviews remained for public viewing. This was unfair to developers that released applications before the review system was amended.
It appears that Apple is retroactively going back and making the AppStore reviews section an even playing field for everyone. All the reviews made on applications by people that never bought the app are being deleted from the US AppStore. All the junk ratings and spam have been removed from the AppStore as of yesterday. This is evident by drastic changes in the number of reviews for various applications on the AppStore.
SEGA's Super Monkey Ball count dropped from 4197 reviews down to 3710 while Namco's Pac Man dropped from 395 to 122.