I think AgentSmith is right that a lot of it is personality of the mod, but I also think that timing and recent events play major rolls too.

(Rambling explanation ahead. Sorry, but I'm somewhat of a native storyteller. If you want to skip ahead I'll mark my conclusion with two asterix.)
I've been a member of Rendo for years, but only recently started being really active in the community again. I all of a sudden had plenty of time, because I just finished school but got too sick to hold a regular job. So art seemed like the best way to spend my time, and get my mind off of pain and discomfort. I started looking at contest and challenges to focus my attention on. Especially the challenges brought me into surfing the forums. Once here I started to notice that it seemed like I'd come in the wake of a major meltdown. And it wasn't just one forum, but forum after forum seemed to be putting out the fires of a massive free fire zone. Some of the language did make me a bit nervous in entering feedback and community events such as challenges. There was so much language of exclusivity (i.e. "Why don't have this or that only open to our community?"; "Why do the Poser people have to butt into our rating system?"; "Those Bryce people don't really understand how to get results out of this program. Can't we keep them out in some way?"; "Man, I hate it when those fractal people post here."; etc, etc, etc.) For me it's odd if I don't use more than one program on a work, I'd say on average it's about three. I thought I might get booed of stage a couple of times, but posted anyway.

**my point: Locking post quickly also might be the effect of a forum trying to recover from a courtesy meltdown.