Sorry, I may have misinterpreted your comment. You are correct, neighboring villages having differing accents/dialects is pretty extreme. I was more refering to the concept of accents having extreme differences, even amongst nearby villages, being a common occurence. Again, sorry for any...
It's not really that extreme. With enough time and isolation, you can end up with vastly different dialects in pretty much any language, and considering Japan's geography, being isolated isn't exactly difficult.