Keeping things under spoiler tags until the episode is subbed is a common practice here and a form of courtesy towards other people who don't want to see major spoilers beforehand. No, it isn't a rule, and if one doesn't want spoilers it is easier to stay away from the thread, but a little consideration never hurt any one.
On a side note - it is impossible for any one to know the future events, because the anime is ahead of the manga. If anything, watching the anime is spoiling the manga for you