The whole point of back-to-back or nested tickets is that you are attempting to circumvent some restriction imposed by the airline in order to achieve a lower fare. Perhaps AA can explain what restrictions in the published rules for your fare you are circumventing? The two tickets may be nested but there are no rules or restrictions in the T&Cs of the tickets that, AFAIK, you are circumventing.
What about routing rules? If you fly LAX-NRT on one RTW ticket and then NRT-LAX on another you are (at least in some sense) using the two tickets to get around the "one Pacific crossing only" rule.