Indeed it should, but the problem (and over the years it has happened time and time again) is that once we get a single thread based on "a small amount of light relief" as you call it, we very quickly have half a dozen. The atmosphere becomes one of "If he/she can post a thread or a link like that, then I will" and before long we have lots of them. Not everyone has the same idea about what constitutes 'light relief' and I start getting dozens of emails asking me why I'm permitting that kind of thread - it's a no win situation.
If I'm to be fair to everyone I have to do what I've just done - post a reminder thread like this. Otherwise where does it stop - do I allow six threads, or ten, and if I allow ten, why not twenty?
Just occasionally it does no harm to deviate slightly from the declared policy, and I try not to jump in with both feet when the occasional 'light relief' thread appears, but if you've watched Speakers Corner over the past few days you'll have seen what happens....one thread becomes two, becomes three, and so on.
I'm here to edit, so I'm editing - hence this reminder.