I don't think it's a surprise that "advertising works". In any market (iOS or bars of soap), spending money up front on commercials/ads/promotion gets you some sales, and the rest happens through word-of-mouth, social sharing, social proof, etc.

$96K is a lot of money to spend if your goal is a top 10 non-game app. Not everyone can put up that kind of money.

And the more people do that (buying installs to kick off a campaign), the more expensive it becomes and more difficult to get in the top 10.