The problem is, it's not even just about catchment areas any more. It's all well and good saying so many people live within an hour of Stansted, but how many of those actually want to use it with what's on offer?
I live 3 miles/10 minutes by public transport from Stansted. This year I've flown from Stansted twice (both on Ryanair), from Gatwick 12 times (on Easyjet) and from Heathrow 4 times (BA and Bmi).
The 2 times I've flown from Stansted have been far the worst experiences. Mainly because of Ryanair themselves, but also 30 minute security queues on both occasions, 30 minute immigration queues late at night coming home, rude staff, etc. On one of the trips, a guy infront of me had 2 bags at security and the security woman was telling him that he'd have to go back to Ryanair and check-in one of the bags. He was pleading with her saying that surely it is is own risk to try his chances at the gate, to which she replied "If you walk off and attempt to join another security line without checking-in your 2nd bag I will call the police". Is it really her job? I'm not really sure of the answer to be honest, I'm sure someone can tell me.
Anyway, I think that the point I'm trying to make is that Stansted has lost it. Is it any wonder that people don't enjoy coming to Stansted, when even I would prefer to go to Gatwick or Heathrow despite them being on the wrong side of London for me? At least Easyjet are consistently average, despite being no-frills and basic they try to make life as easy as possible for the customer and you know exactly what to expect each time (nice website, decent mobile phone app, not too much emphasis on selling you stuff on board, no silly tunes played on landing, no embarrassing J20 adverts played on boarding...etc). With Ryanair I just have no idea how cr@p my flight is going to be, my last trip on them was so dire that it actually put a downer on my entire weekend away.
Unfortunately with Easyjet cutting back at Stansted it will only mean more and more trips to Gatwick for me.
And as for the train line...I commute on that line daily to London on the Stansted Express and at a guess I'd say that approximately once every 2 weeks it has some kind of signal failure where I have to sit there watching various tourists pull their hair out over missing their flights and panicking about how much Ryanair are going to charge them for new tickets on the day. I imagine that each and every one of them who has been through that experience would choose to avoid Stansted on any future visits, and recommend the same to their family and friends. I hate to say it because I worked at Stansted during it's peak around 2008 when everyone really seemed to be enjoying themselves, but I can only see the passenger numbers continuing to drop for the foreseeable future.