I'm not sure how clear the sum of the replies have been.
Afaik (based on several booked and completed OWE's) there is no reason to include an unused segment showing you returning to your originating city, mgm's quote of a rule notwithstanding. Your booked itin will have to show a segment that returns you, as exmo said, to the country or region from which you started.
(On the other side of the coin, while we're talking rules, remember that you are not allowed to pass through your originating city near the end of your rtw. If you start e.g. from LAX and fly back into LAX (or co-terminals) your trip is over. So if you intent is to fly some additional segments in the country of origin be sure to return, in this example, to SFO or some other place.)
[This message has been edited by JohnAx (edited Dec 22, 2003).]