The problem Newcastle has, is that the catchment area population is significantly smaller than that of Liverpool, Bristol, East Midlands, and even Belfast. Never the less, whilst these other airports may have huge LCC presence, Newcastle is coping quite well with a good mix of LCC (Jet2, easyJet, Ryanair, Flybe), Charter (Thomsonfly, Thomas Cook etc) and Legacy carriers (BA, KL, LH, AF, SN/BMI, EK).
How many of those other "similar sized" airports can claim to have a successful daily A330 service to Dubai for example?
