One problem with this is that the comments may no longer be relevant/accurate once the story is changed.
Let's use a non-technology example:
Let's say at the beginning of the NFL season, an article is written about the Green Bay Packers and their Week 1 victory over the Seattle Seahawks. Lots of comments about both teams, their players, the game, etc. After Week 2, the article is updated to reflect the Week 2 loss to the Atlanta Falcons, with only a minor reference to the Seattle game. Now people comment on the Week 2 teams, players, game, etc. and the comments from the Week 1 game seem out of place. By week 17, the comments are a jumbled mess. While the topic might be the Green Bay Packers, the fundamental statement of the article has changed from GB defeats SEA 17-9 to GB loses to ATL 23-34.
Returning back to the MacRumors forum and other technology Q&A forums.
You can see the confusion in some forum postings where the original post is edited and some comments end up being puzzling because they refer to something that wasn't in the revised post.
Also, other sites may refer to any given article. If the original article is edited, it may render the link/reference incorrect.
Issuing minor corrections is considered acceptable but not changing the topic of a published work.