AA doesn't "want" (prefer) this, it requires that either TATL or TPAC be on an AA marketed flight if you book through the AA RTW desk. While I recall that one FTer once claimed that s/he was able to book there without an AA marketed trans-oceanic flight, the agents have always been clear with me that it is a requirement. Note also that this does not depend on the routing actually flown. For example, CX JFK/BOS-HKG is considered TPAC even though it nearly always flies eastbound (due to the jetstream).