I don't know what airline you worked for in Europe but I can assure you after 10 years working in the UK my airline used to routinely cancel flights that were not full enough. Especially if it could be consolidated with another service later in the day. We had quite a few long haul services get cancelled from time to time due to lack of interest. Is this not what the 'green lobby' in the UK were demanding and the whole idea behind the loosening of the rules on 'slot' regularity out out LHR at the start of the credit crunch. The new rules allowed for 'tactical' cancellations without putting the slot pair in jeporady. I am certain that most airlines who are able do it.