Thomsonfly,
This relatively new EU law on compensation is an absolute disgrace, and is another way in which the airline industry is discriminated against by the bureaucrats in Brussels.
In an ideal world airlines would keep spare aircraft and crews to the extent that the cost of keeping those spares was less than the total cost to passengers of the delays and cancellations which could be avoided thereby.
Given that some airlines are not noted for idealism, one way of ensuring we get as near as possible to the ideal world is to ensure that airlines pay an appropriate level of compensation to passengers, and can in consequence determine exactly how much a spare aircraft might be worth.
Discrimination doesnt necessarily come into it !