I can't understand, is storing pure text too expensive for IMDB which is owned by Amazon which runs half the servers of the planet? Why don't they keep the threads while disabling new discussions?
If you are certain that the post has been deleted and you didn't do it, then there are two possible reasons: the message has been removed by a moderator or it has expired. Our boards are not designed to store messages indefinitely: after a certain amount of time older threads are removed from the board automatically. This process is called "expiry".
The rate of expiry is adjusted dynamically according to the posting traffic for each board. Threads are removed sooner from a board that attracts a lot of posts than they would be from a board with less activity.
Please keep in mind that the boards system is not meant to be an archival medium, and all posts are subject to expire and disappear sooner or later. This is intended to allow us to manage the resources consumed by each board effectively, and also to promote the ever changing flow of discussion.
I've battled spam at another film site. If my experience is anything to go by, even mentioning the word "spam" is enough to make smoke come out of the operators' ears. They tried to delete the spam and abuse when it was posted, but some slipped through and leads to new support requests and new complaints even now.