Apple has made some significant background changes to the way iOS apps are ranked on the App Store, according to several pay-per-install and mobile ad networks. In particular, Peter Farago -- VP of marketing at analytics firm Flurry -- notes that in the past several days the Top Free rankings in the US have shifted unexpectedly. Facebook recently climbed to first place for example, despite having earlier floated between 10th and 20th for over a year and a half.
