Whilst that is true, easyJet normally have a sufficient number of spare aircraft and back-ups around the UK and Europe. Add the fact that in winter they have a reduced flying program compared to summer.
I'd say a 12 hour delay isn't really justifiable, easyJet could have found a spare aircraft, re-arranged other flights and used a spare.
But, this is not as easily dealt with given the strict deadlines imposed by EC 261/2004 for Type I and II flights. Fully agreed that if the sole reason for delay is the unavailability of a spare aircraft or crew to operate it, 12 hours is likely unreasonable in Western Europe, that is not the case for Type I flights where compensation kicks in far short of that.
Each "knock on" must be examined for its own facts. Where did it occur and under what circumstances? Even 60 minutes flying time away, the fifth spare may be hard to locate.