Here I would have to agree with VintageKrug, It just doesn’t seem possible to get around the flexibility issue for airlines such as BA / LH / AF.
And comparing Asia and N.America doesn’t seem right – it’s apples with pears, not apples with apples.
Asian airlines tend to use long-haul widebodied aircraft across their fleets and therefore they are used on both short and longer flights. To some extent this could be argued as also exercising flexibility in an inverse way – they also want to keep fleets rationalised in order to use the same aircraft across as wide a route portfolio as possible. And many have opened LCCs to enable shorthaul aircraft to enter their fleets.
In NA, it is the biggest air network in the world (still – I believe I read that somewhere) and so the numbers of flights and aircrafts and hubs that each airline offers allows them be able to have fleets just dedicated to one or two routes or hubs alone, e.g. NYC-LAX / SFO