This is a hidden secret of the "App Store economy". To see how strongly the "Hot & New" dynamics are embedded into App Stores, check out the sections of the iOS App Store (Featured -> New & Noteworthy) or Google Play (Top Grossing New Apps)

If you are able to catch onto a foothold, you can reap a lot quickly - but the fall will be just as fast as the author saw here. The apps that are able to stay on top have a very strong hook with increasing value (ie the popular social gaming apps with in-app purchases or the social/messaging apps). Anything else will result in the inevitable fall in rankings and therefore sales. This is why "app development companies" often have many many apps in the app store to continually reap from this cycle. There's another aspect to the publishing cycle and it's in-app purchases. The #1 paid app on the iOS app store is #31 top-grossing. 28 of the 30 before it are all free apps (which aren't ranked all that high in the free charts)