This is a very good question!
The filed rule is quite ambiguous:
Code:
50.RULE APPLICATION AND OTHER CONDITIONS
AA/AY/BA/CX/IB/JC/JL/JO/KA/LA/LP/MA/NU/QF/RJ/XL/4M
ONEWORLD
EXPLORER FARES
APPLICATION
[...]
BAGGAGE REGULATIONS - THE PIECE SYSTEM APPLIES TO
PASSENGERS TRAVELING ON A ONEWORLD EXPLORER FARE.
Incidentally, my interpretation of AA's rules at
http://www.aa.com/aa/i18nForward.do?...eAllowance.jsp is that yours is an international
itinerary and that therefore you fall in the "Travel to/through/from Europe and Asia" or the "Other International Travel" category. As such you don't have to pay for baggage check-in on any AA segment (whether it's a domestic flight or not) in the qualifying
itinerary.