In the configuration section of Movable Type there is a field to fill out the number of days to retain posts for. It was set to 7. So, everything older than 7 days gets dropped off. Pretty stupid if you ask me. I set it to 30. I think that as much as I post, which is probably 30 times/month at best, having the last 30 posts displayed is about perfect.
Third Generation Steelmaker