I wonder why the CH team doesn't lock old threads? I've come across a few threads where someone posted 2-3 years ago asking for restaurant recommendations for a special occasion or for advice on some food etiquette. There will be the usual flurry of responses at the time and then nothing for several years until someone (perhaps new users excited to discover CH?) somehow finds the thread and posts a new comment - which then puts the thread back at the top of the board. This usually gets more people commenting on it, not realizing how out of date the thread is.
Why not lock up a thread after a specific period of time, esp if the topic is time sensitive? Or provide a way for the original topic creator to lock it, esp if they've received the advice and/or recommendation they wanted? IMO, it would help keep the boards tidy and up to date.