Right, but forums are a much slower, more "official" communication medium, so the edit feature makes more sense.

I see chat like in-person communication where editing something already said is impossible.

I think we're at the vi/emacs point of this discussion. Editing messages works well for me and my team, and we're glad of the feature. You don't have to like it, and I wouldn't force you to edit messages. The world supports both and we both win. :)