Exactly. Transfer desks at international hub airports exist for this very reason. This has nothing to do with specifics of AA, IB, or oneworld. I've traveled on many airlines in all alliances where I could only obtain some, but not all, boarding passes at the initial check-in. This is due to various reasons, such as: checking in earlier than T-24hrs of later flights, poor IT links between various systems, varying check-in rules (time, documents, needing to be present in person, visa requirements, etc etc).

Seems like there are bigger (actual?) problems we could be spending time and electrons discussing....