LTNman's story may well have some validity in that it might be understandable if easyJet were driving up SEN-AMS prices to see what the market would stand.
But then flight times from SEN to AMS are shorter than from the other London terminals, and landing fees at SEN are rock bottom (if we are to believe what we are continually told) so operating costs from SEN should be lower and this should support a lower fare structure.
Does easyJet really know to what extent those "artificially low fares" took customers away from their own parallel routes, and to what extent they won customers from their competitors ? And to what extent those supposedly low fares encouraged people to fly who otherwise would not have felt able to afford it ? Perhaps this is what they are trying to establish.