Yes, rules are rules. You should only post on the correct Board.
However, I seem to be seeing more instances of posts languishing unanswered on "wider" (e.g., Pacific Northwest) Boards, while the technically "improper" duplicate post made on the "narrower" Boards (e.g., Seattle) gets good responses.
A classic example of this is the poster who asks for resto recommendations in the San Juan Islands. How can a poster get meaningful responses *without* also posting on the Seattle Board?
I this vein, just yesterday a thread on Pacific Northwest (from 2007, with lots of good info about oysters) was locked, ostensibly because it concerned Portland.
Why the strict Mod concern over geographical correctness, if the idea is to get replies?