Since I’m the one who made the change highlighted in the OP, let me explain my reasoning.
Generally speaking, the policy of the SDMB is to minimize changes to posted comment. We’ve relaxed a bit, in that there’s a five-minute edit window for example, but the board is supposed to contain your words, not those of the staff.
That said, there are times that we need to make changes (e.g., breaking NSFW links or “call to action” posts), or make changes to be helpful (sometimes at the poster’s request, sometimes on our own). Sometimes this means changing a thread title to be more meaningful, fixing an error at the request of the OP, fixing goofed-up coding, or moving threads from forum to forum.
I’m a big fan of transparency. When I change someone else’s thread or post, it leaves a trail that other moderators can follow but the membership at large can’t see. So to make it clear to everyone else, I mark my changes.
When I move a thread, I make a post saying where I moved it from and to. That way, if someone sees a sudden change in tone in the thread, they’ll understand that it’s because the thread changed from (for example) GQ to the Pit, where the rules are different. I do the same when I edit posts – you will know not only that your post was modified, but who did it. That also means if I screw it up, you’ll know who to contact.
So, getting down to thread titles, tagging the title change and including an explanatory post accomplishes the following:
[ol]
[li]It maintains continuity and eliminates confusion if people made direct references to the old title.[/li][li]It lets the OP know who to contact if my change was inappropriate (e.g. inadvertently ruining an “in joke” or a pun).[/li][li]In this case, it reminds people that threads with informative titles get more views and better responses.[/li][li]It helps to keep the whole moderation process more transparent.[/li][/ol]
There is no fixed rule or mandated procedure on this, so other mods handle this kind of edit in their own way. I never make such edits with the intent of pointing out someone’s error or ridiculing them. I would consider that abusing my position as a mod. I’m just trying to do my part to keep the SDMB a smoothly running well-oiled machine.