Dont sweat it out. I read that theregister.co.uk article in depth and I am going to quote and give you an explanation. ok.
"A blog owner can avoid liability for user-generated content that appears on his site without being checked or moderated, the High Court has ruled. But fixing the spelling or grammar in users' posts could lose him that protection, it said."
- the operative word here is "fixing the spelling or grammar". Keep this in mind.
Now the article's summary:
1. A blog owner had a few articles.
2. a Libel comment was made in one of them, not by him.
3. instead of deleting that comment, he edited
the spelling and grammar.
4. he got sued, for libel, from the affected party of the comment.
Now when you edit a comment or article you are basically putting your stamp on it, you are endorsing it, this is the ruling of the court. The blog owner was a little naive, foolish, didn't care or a bit of everything; he should've deleted
the post not edited it, and most important, he changed the spelling and grammar and not the offensive, libel bit. Fail.
Coming back to your forum: If you delete offensive comments you can't be held responsible for the comment at all, in fact you are doing exactly what the judge thought the blog owner should've done. Read the ruling. But if you edit the offensive posts and leave the offensiveness there(this is important) you can be held responsible, because according to the court, editing content is equivalent to endorsing it.
So, important, don't edit a post and LEAVE the offensive bit in there. Don't correct spelling and grammar and leave the juicy bits there, edit out the offensive stuff.
I am not a lawyer, as yet. but have family background. dad's in gov, uncle's a lawmaker, etc etc. I am pretty sure of what I am saying and it'll hold in court, though you should'nt ever want to go to one.