It is a requirement for using storyboards that your application delegate inherits from UIResponder and that it has a UIWindow property. If you look into AppDelegate.m, you’ll see that it does absolutely nothing. All the methods are practically empty. Even application:didFinishLaunchingWithOptions: simply returns YES.
The secret is in the Ratings-Info.plist file. Click on Ratings-Info.plist (you can find it in the Supporting Files group) and you’ll see this: