When in the industry, I made steady commission checks sending our crews out to replace rotten posts in the PA, NJ, MD, and DE region (my territory at the time). Youngest building was 5 years old, oldest was 70 years old. Most were in the 15 year range.
It is what it is... people will believe through and through that it can't happen to them, and I hope they're right. But to me, a little extra per post (about $2,000 for all the posts in the example noted above) to be absolutely certain you'll never have a problem compared to the total cost of a build is in the "why on earth would you do it any other way" category.
Side note... from a real estate resale perspective, permanent foundation (either stick build on poured or block foundation, or post-frame with perma columns or similar) is a selling feature. I know that I wouldn't buy someone else's old pole barn with wood in the ground. I've already fixed a barn (on my property) where all (yes ALL) the 10x10 posts were completely rotted through.. Fool me once...