Good questions sir! Ones I have been pondering myself! I tried looking through the Shogun folder to see where this info is held, but alas I could not find it.

Early though I read that getting a Swordsmith (+1 weapons) will upgrade hand to hand weapons only, so Archers will be not be more deadly with their bows. I don't really think this is historically accurate as arrow tips were made from sword steel, so with improved weapons you should get better quality arrow heads (better armour penetration?).