Dom Esposito of AppAdvice has discovered a bug in iOS 7 that allows you to put apps inside Newsstand.
He explains how to put apps in the Newsstand app:
First, put your apps into wiggle mode. Next, drag an app on top of Newsstand and slightly wiggle it or hold it there until you see Newsstand blink. Newsstand’s natural instinct is to make a folder, but if you hold it there long enough, it will open and you’ll be able to place the app inside.
He has also created a video to demonstrate how it works:
If you want to remove the apps from the Newsstand, then all you need to do is reboot the device.
It’s quite likely that Apple will fix the bug in future beta versions of iOS 7, but it seems like a cool trick to hide the stock iOS apps.