This is kind of high trust vs low trust society issue, smaller more homogeneous forums can do with fewer rules and less mod involvement, while larger less homogeneous boards need rules for every little thing and lot of mod involvement, which can quickly spiral into purity mode.
The necro rule is due to griefer tactic which I saw several times on different forums, basically spamming the first page with long dead threads, usually the new post was as little as a single dot, but later when minimum message length was enacted, they turned to copy-paste a line or two of text. It looks like shit like this was common enough for these measures to be made a default part of forum software. I have no problem with mods granting these members their suicide by banhammer wish.
And don't get me started when seeing a new reply on a story that has been on hiatus for months, hoping things are moving again only to find some moron asking why there are no updates. Pile up of pissed off members telling the moron where he can stick his query is fine, no need for mod intervention.