In my area, my competitors and my business, we do not do this peir thing. First thing, its expensive, second the hole has to be so big, secondly wood will not rot anyway.
Case in point: I installed a fence on my property 35 years ago. Since that time I have replaced the fence twice. But, there has been one post that I could never get out and I always decided to just leave it. To this day, that post is as good as the day it was drilled and cemented in the ground.
If done properly, for instance drilling an extra wide hole, going down 24 inches for good fitting, then dropping a brick in the bottom of the hole, then setting the post on that brick, anchoring the post in the ground, pouring the concrete in the hole, messaging the crete, then making a cone shape above the ground for water to drain off, that post will last forever.
Now, ice, and frost lines do not have any bearing in our area.
Code Enforcement is the best way to decide upon which procedure to use. Code in my area will allow the above procedure, but I bet in the East, you have to have your piers.