This is true, though there's no practical reason that TBIT or ORD T5 could not be used for domestic flights. In those cases, the reason they are unavailalbe to domestic travellers is that they are not connected airside (excepting some bus services). In fact, AA will have a direct airside connection between T4 and TBIT in not too long, at which point it will be possible to use the TBIT lounges when departing from T4 (assuming one has lounge access, and unless lounge access rules change).