Wiggy, what it comes down to is, that commercial financial pressures have forced the operating regulations into tight corners. In your "longhaul arena" you might see contingency fuel giving you a large "comfort blanket". It can be different on shorter sectors.
We can make-up scenario's of aircraft unservicabilities and weather-clamps but, the basic fact is that the present rules pretty much rely on the weather forecast being right and the aircraft staying servicable for the planned approach CAT.
