It is actually. By commenting on old questions or changing old answers you are mearly bring up old topics, it's pointless. Many of these discussions were made when he didn't have the same kind of information we have now, such as a year ago for instance. Commenting on old questions with new comments is like going back to an old conversation and bringing up new ideas, it only serves to distract from the current conversations. If you want to talk about new changes in old topics, I suggest you make a blog post.
I don't think we wrote any policy that says you aren't to reply to old questions. However you have to use discretion: if you need clarification or more info on an answer, then that's fine. If it's for anachronistic reasons to say "the answer is wrong", continue a dead topic or whatever then no, that's not necessary.