I do take your point on school holidays and the like, living in Scotland also seems to be penalised - we always head south over the border and fly from Manchester/Newcastle - as the school summer holidays are earlier up here we fly from England before England's school holidays have even started. This doesn't save us a small amount, it can save us anything up to £800 for the four of us!
The truth is that flights are not any different to anything else, it's all about demand and supply. You can't blame them for that even though it hurts. Where we all fail is that we can be flexible on departure airport but never on arrival airport - we all want to land at Dalaman. If we weren't so specific there are some amazing prices to be had. We can fly to Prague from Edinburgh for around £70 return with Jet2. It just seems that Dalaman rarely throws up any good deals from any airport around here.
