What's now swimming to the surface is the service level differentiation and the concept that bmi's been "over delivering" (So sez young Nige) - buy the cheapest fare and the first human interaction with bmi you'll have is when you board the aircraft. You HAVE to book via the internet, you HAVE to use a check-in kiosk.
That's where the savings are.
And as for self-catering - I always pack a lunch,even if I'm on a firm Business ticket on longhaul. (How often do you get downgraded to Economy and end up weak with starvation by the time you get to LAX. Mind you, it's a hard call if you get a First upgrade - bacon sandwich or caviar....!)