My understanding is that some awards on other partner carriers permit AC travel to their gateway. For example, an Air New Zealand award would include equivilent class AC flights to/from LAX or SFO (if they still fly from there). Similarly, a UA award to Asia (or anywhere) can include AC travel in equivilent class to nearest Canadian city where UA flies, or to its nearest gateway in the U.S. Flying to Europe, I believe you can have connecting service on BD out of LHR and LH out of FRA or MUC within the country of immediate region [i.e. within Europe]. You are correct, however, about needing separate awards if you want to travel outside one of the regions AC flies to, and I believe also for connecting travel within Asia.
One of the things I was hoping we would see in this new membership year was a STAR Alliance award chart, integrating trips on two or more carriers in the same fashion that oneworld offers based on mileage lengths to be travelled. We were told this was in the works back in July at our meeting with Aeroplan folks.