There is a post filtering option down at the bottom of the forum section that is set to show only topics that have been posted in during the last 30 days. If you want to see everything, then you must go down to the filter and change the selection from "last 30 days" to "show all". It's a simple way to keep the forums cleaned up without having to do any work, but it seems to confuse a lot of people. Things aren't being deleted, so please don't worry about that. Maybe I should make up some kind of FAQ write-up on the filter thingy so that everyone will understand how it works?
BTW, excellent work Yuzuki-chan, I love it.