Back before the railroads, which were the first genuinely fast mode of travel on land, all major roads had inns along the way, something like 20km apart, depending on the road condition, place, and terrain. Did Japan have whole towns (villages?) founded around these inns? It's not like such a thing couldn't have happened anywhere if a certain place had special benefits from major traffic, but to call it a post town means it's not just an inn with a stable for the travellers' horses.