The 5 mile rule applies to many types of businesses. Why? Because people want to purchase locally. They don't want to drive 2o miles for insurance when there is an insurance company 2 miles down the road.
If you were to plot your customers on a map, you will find that at least 85% of your customers do not travel more than 5 miles to get to your business. So, why would you spend advertising dollars over 5 miles away? You shouldn't. You should advertise locally and make sure that you're not wasting dollars on trying to get people to travel to your business.
I use this rule in my own advertising and when I advertise for my customers. This is a great advertising "rule of thumb" because it will save advertising dollars. If you think of the distance that you would normally go to the bank or other retail shops that you frequent, chances are, nothing is over the 5 mile mark.
There are a few exceptions, but not many. It really depends on the type of business you have and whether you can talk your customers into traveling.