To provide you with an answer, a thread about an active prosecution could breach the Sub Judice rules and therefore the site owners (and posters) could be held for contempt of court. I would imagine it's safer to delete it than to run the risk of posts breaching the rules.
As I understand it, the press are allowed to report on what was said but not say anything that could sway the jury either way - ie 'the prosecution allege that Mr A did this on this date' or 'Mr A claims that his accuser is lying racist' - but they can't give a definite opinion on it (ie, they can't say Mr A is a filthy child rapist until he's found guilty).
Yes they can read newspapers etc however depending on how well reported the case is they may be asked before the trial whether they've read anything about it and if they have they may not be selected for that jury. They may also get a warning from the trial judge not to read anything that may influence them during the trial.
The media are bound by the same rules, however they do often sail close to them. In the interet/smart phone age it's getting much harder to regulate sub judice. For example, we could all sit in a pub and chat about a case and that would never be contempt of court (as long as we're not part of the case) as the jury would never hear our discussion. Today with on line chats, faceache etc it is much more difficult to prevent juries being influenced.