Originally Posted by dagSD
there is no rule that requires you to take all of the flights on your itin. You can book a OWE that starts and ends in Europe, and just not use the last leg.
I would disagree. Rule 4 in the "Application" section lists the instances where you can begin your trip in one place and end it in another -- you can do so within Africa, the Middle East, South America, and a few individual country combinations, but not Europe.
As has been mentioned by several others, an airline issuing a OWE could theoretically pursue a customer who does not complete a OWE, seeking a total of the charges for each point-to-point flight.