This is possible, but it's so difficult to enforce that I assume it must be a reporting error. Will the dropbox app prevent me from accessing more than 2GB of my folder? Will they force the Pandora app to keep playing music after 40 hours even if haven't paid for a subscription? Will I now have to buy a separate Netflix plan for my iPad that I buy in iTunes instead of getting that with my regular plan?

The minute you allow any sort of third party authentication systems in an app, it becomes basically impossible to know whether or not someone is using those credentials to buy something on a website somewhere that enables access to more data in your app.