So any airport is only as useful as what you want to use it for....
Quite so, Pegpilot. I believe there are many unnecessarily circuitous journeys made. Not everyone is travelling from city centre to city centre.
Let's take the London to Frankfurt example. For passengers starting their journey in London's Trafalgar Square, a journey to either Heathrow or City is easily achievable. Similarly, those heading for Frankfurt's centre will be well catered for by Rhein-Main Airport.
However, someone from Colchester going to the German town of Trier might be better suited going Stansted to Hahn, rather than trogging across London and Frankfurt unnecessarily.
On most flights you will have a mixture of both centre-to-centre, centre-to-rural, rural-to-centre and rural-to-rural passengers.