Rubberized Post Base Bottom Protection
This isn't a bad idea and you can clearly see that the
building contractor or home builder actually went the extra mile, by
trying to protect the bottom of the post base by installing a rubberized
product to separate the concrete from the wood.
Something like this will definitely prevent any moisture that has been absorbed into the raise concrete post base, from coming into direct contact with the bottom of the wood post.
I don't really know how effective this type of construction actually is, but it obviously wasn't the cause of the bottom of this post rotting.
Here's a picture of the post base after the water damaged post was removed.
Home Repair Tip: Whenever you run into a situation where the wood post is damaged, like the picture above, make sure that you clean these areas properly before reinstalling the new wood post.