Marcus it does not make sense to complain that it is more expensive to fly from LHR as opposed to AMS, of course it is, it is more convienent. I just took a quick look and for comparison….
BA LHR-LAX direct £3100
KL AMS-LAX direct £2900
KL LHR-LAX via AMS £2700
BA AMS-LAX via LHR £1800!!!!
So that Dutch family could be complaining that KLM is just trying to fleece them by over £1100 per person.
It is just market forces, direct is always going to be more, and it will always be cheaper to go via somewhere else as that airline will have to try to entice you somehow, or you would never take the longer route.