Why is Puerto Rico included on Country Table?

Why is Puerto Rico included on Country Table?  And how have other customers handled the PNA requirement that PR addresses have USA country code for proper tax reporting?

Right now our payroll department manually changes employee's country codes from PRI to USA. Are there any delivered methods to do this or to prevent employees from being able to select PRI?

From PeopleBooks:

Note: Payroll for North America requires the person to have one address with type Home to successfully calculate taxes. You must set up each Puerto Rico employee's home address with country code USA and state code PR for proper tax reporting.