Kuala Lampur, June 22 -- Aviation watchers already saw it coming: Spirit Airlines has closed its doors. The immediate reaction is to blame the familiar bogeyman - the Gulf War, the spike in crude prices, the geopolitical dominoes that send jet fuel costs rocketing past the stratosphere. And yes, the war is the spark. But let's be clear: the fire was already burning in the engine room.

For months, we have watched airline CEOs wring their hands as fuel prices dance to the tune of distant missiles. Now, with Spirit Airlines - a carrier built on the brittle bones of ultra-low-cost efficiency - becoming the first major US casualty, the industry is finally asking the question it has dodged for decades: How do you build a business model on a re...