Apple wants to try to keep apps that pretend to be something like, oh, Halo 4 from submitting an app then changing the screenshots post-approval to look like the fake game.
Posted in a developer bulletin today and noticed by MacRumors:
Beginning January 9, app screenshots will be locked in iTunes Connect once your app has been approved. New screenshots may be uploaded when you submit a binary for an update to an existing app or a new app.
From: Mac Rumors
This change is aimed at ensuring apps that are submitted and approved don’t try to pull a fast one on app shoppers later. MacRumors explains the scam like this:
For example, in one instance, an unofficial Pokemon Yellow app was uploaded to the App Store. The app snuck by Apple using an unobtrusive set of screenshots, and then switched them out with photos from the Nintendo game, which thousands of people then purchased.
While Apple has in the past refunded money to people who bought scam apps, it would probably just rather nothave them in the App Store in the first place.