Not always the case. I considered flying Air Asia to KL form Stansted. When you added in all the hidden extras, I could have got a similar deal flying with the regular carriers.
Last time I flew Air Asia was in January from Kuching to Kota Kinabalu. Did the online check for wife and I and we were seated two rows apart. Not a big issue for a one hour flight, but I believe Fernandes does this deliberately to increase revenue. I can afford the extra five Ringgit but Malaysian families might baulk at the extra costs.