Originally posted by Lonewolf:

As your archery skill increases, it doesn't get any easier to aim. You just draw the bow faster and use less stamina.

I don't think that's quite correct. I found the crude bow to have terrible aim with massive drop, and all the subsequent bows to be much better in that regard. It's true that that is unrelated to skill, but the hitbox is still related to progession in my experience.