No idea about KLM
The service on LH long haul (LH LH??) is pretty similar to BA. I find the seats worse (think BA domestic for 9 ho) but no doubt others will prefer them
as other have said, you probably get a better price for the same reason it cheaper to fly with BA from Oslo to the US via LHR than to fly direct from heathrow. the providers realise that your time has a value and the extra travel time means they compensate by reducing the price