Genom-X You stated one very important thing in your own post already:
While I do find the necroposting rule rather...questionable, the way it is stated is more or less yet another anti spam rule:
15: Do not "necropost" in discussions that have not had a reply in
over a month unless you have good reason to believe that your reply
will be of interest to the original participants...bla bla bla...
4: No Spamming or "post farming" - Do not spam threads or spam comments without constructively adding to the conversation.
It´s essentially same just formulated differently.
I´m not gonna make any statements about wether I think "hmmm..." is something that constructively adds to a mod thread or not, as this is more about the rules than the former discussion.
Also, I´d guess we´d be stuck somewhen around the Middle Ages.