Thank you for the question.
When I said that we have different retention periods for different items, the reason is that we keep information for different purposes. In general, we want to have information in our records for only as long as it's needed to provide services. For example, if you post something on your timeline, there's no fixed retention period that's associated with that. We leave it on your timeline as long as you leave it there, and if you choose to delete that content or delete your account, then we begin the process of removing it from the various places on our service that it exists.
There are other pieces of information for which we have a more routinized data retention process. I referred earlier to social plug-ins, which are the light buttons that you see on various places on the web. In those cases, for logged-in Facebook users we store it for 90 days, and after that period we either delete or anonymize those pieces of information as well.
So different pieces of information are subject to different processes, but we try to be thoughtful about the way in which we retain the information.