I have read and re-read the Help section on Approval Routing and I am still confused as to how PO routing is supposed to work.

Here is another thread raising the same basic issue:
Custom Employee Center

I think the main confusion is WHO is supposed to be the final employee (after all required approvals) who actually processes the PO (sends it to the vendor(s))?

The Help PO Workflow Chart shows such an employee, but does NOT provide any text describing how this empoyee (let's call him/her the Purchasing Agent) receives or is notified about approved POs. This chart could use some clarity as it shows "employee" as the action person for all blocks, when in most cases, it is a DIFFERENT employee who actually performs the action.