<dons moderator hat, positioning it with a rakish tilt>
We can un-stick threads on a case-by-case basis, if someone has a good reason for requesting it. But as dekh says, they are generally sticky for a reason, and many of those reasons don't have any particular expiration date.
If anyone does have a specific reason why a thread should be made sticky or unsticky, feel free to post it. Or if you prefer, you can send a message to a staff member about the matter. <removes moderator hat, smooths hair down, and throws hat into the washing basket>