It's not forbidden to make jokes or put a bit of humour in here. In fact I'd say it's welcome indeed.
However, there are kinds of jokes and humour that are very much an eye-of-the-beholder thing.
Your jokes may make some people laugh out loudly, they may make other people angry. Even though they can clearly see your smilies or sarcasm tags...
Imagine my signature would read "Only Losers Use Windows". Now imagine you'd like Windows as much as you like Macintosh.
Back on topic, however: I don't think the crackdown is meant as a warning just before MWSF. Apple has been very strict about leaks before, and whenever they can track a leak down, they're quite aggressive. But I think that's also quite clear, because much of Apple's successes in recent years have been surprises. The PowerMac's stats were open to the public much too early this past summer.
And I must say, although I'm in the business of rumours myself, I enjoy every surprise Apple can pull off without us knowing it beforehand was worth it. Remember the first iMac. Remember the iPod. Or the TiBook. Those were all very well hidden from rumour sites until presentation.
