Norwegian didn't start in 2007. They go back to the early 90's.
Re: leasing. This is true of virtually all airlines these days outside of some flag carriers - I was being sloppy with my wording :) However, you get much better lease rates if you're willing to commit to a very large order and are negotiating it during a downturn. Which is what both Ryanair and Norwegian did.
Airline manufacturers and leasing companies traditionally experience a large drop off in their deal pipeline at the beginning of an economic shock/downturn because most airlines are badly run, cash strapped, slow moving and have no appetite from their creditors to commit to multi-billion, multi-year leases just when the wider economy is going to shit (and hurting their passenger loads). Non-legacy airlines (mainly budgets) have more tools available: they quickly drop routes, slash staff count etc. to ride the downturn while at the same time investing for the inevitable swing back. Helps too that they are the last to be hit by falling pax numbers since their ticket prices are so cheap.
There's lots of other factors at play too that I haven't really touched on. How an airline hedges its fuel and forex, what deals they have with airports, which manufacturer they standardise on (Boeing or Airbus), where they get their crews from, how they retail their tickets, which markets they're strong in, what AOC(s) they have, who their investors/creditors are (state, bank, sovereign wealth fund, pe, private) and on and on and on.