I'm not sure I understand why some requests are closed, and others aren't... HubPages requests, for example, from 6 months back... some are still open, some are closed. And it doesn't seem to have to do with how many responses they have either.
Those older HubPages requests were actually from the old "IdeaBank". In order to keep the Idea Bank fresh back then, we frequently retired those topics that had been addressed by at least one good request.
If there's a topic you think you can do a great job on that ought to be reopened, let us know and we can reopen it for you.