The hub argument is purely based on connectivity. One passenger may travel from the US, via LHR and on to HKG for example, never actually setting foot in London. However, another passenger on that same flight to HKG from LHR will be based in London due to the connections with HKG. Each of those passengers individually does not justify the route economically to an airline, but combined it enables airlines to put on the route, thus providing connectivity both to transit and point to point passengers all on one route (ignore the actual destinations, they are just an example!)
It is the very reason why Qantas have just signed a deal with Emirates to fly though their Dubai hub. Why else would anyone fly to the desert?! The answer is that, from DXB, you can connect to pretty much every European city via a direct flight, meaning that any city in Europe is within one connecting flight from any city in Australia, which is pretty powerful route planning.