Pokepal: Neither the time or the place for that.
Khush - it is possible and it is something that is still done occasionally (usually just moving a post from Talkback and merging it into some various Funhouse thread). However, I'd like to point out that the last time I talked about enforcing rules by trying to keep topics actually on-topic, not a single person on this forum spoke up in support of that plan. In fact, the mere mention of it eventually lead to at least two members becoming so disgruntled with the forum that they left and took refuge on their own forum where the forum maturely spend so much energy talking trash about all the other video game sites out there.
So... what to do?
Well, I never saw that thread before.
My answer on it would be is that it is all case by case. I mean, topics do go off topic a lot of time because that's what conversations do. They morph and change into new things and that's not necessarily a bad thing.
But I'd say in the instances like Shyguy mentioned in his original post where somebody will take something and post a picture or joke that sort of breaks the rules or causes the thread to be locked should just be pruned since it will add nothing to further the thread and would just end up killing it. Yeah there will probably be complaints but if a person keeps having such posts cut, chances are they won't think it worth the effort and that kind of stuff would drop off.
It's sort of like officiating in sports, I guess. You're always going to get complaints from both sides for the job you do unfortunately. Still, as long as the rules are enforced consistantly, then the flack will be less as the players adjust and learn what is acceptable and what isn't.