I wouldn't know, but from what I can guess, not a whole lot of apps need to be sold. Just someone at Apple needs to see a good quality app and I'd guess suggest it as a featured app. It seemed no one knew of Active Money Pro till Apple Japan featured it, then it skyrocketed from just another finance app with a dollar sign as it's icon to the most highly rated finance app in the Japan iTunes store. It's still not number one, as it's on the pricey side as apps go, and most on a fixed salary just feel they need a good cheap expense tracking app. It's currently number three though.