Now entering new city, population unknown

Which brings up the question of why population figures are on the signs at all. If a city needs to replace a sign simply to update its population total, isn't that just a waste of money?
Or is there someone out there who sees a sign that says, "Now Entering Cityville, population 182,000" and decides not to stop because the population isn't quite 200,000?
Maybe Sundance above is a huge metropolis by now.