Not quite answering the question posed, but I do want to posit that air passenger traffic has continued to grow steadily nearly every year since it began: http://data.worldbank.org/indicator/IS.AIR.PSGR

There are a lot more people flying and/or flying more and that could increase the complexity of travel. Also, increased security can lead to more variable wait time and thus another variable to consider more now when deciding on what time to leave for a flight. Perhaps the increase in flight apps allows more efficient travel planning and thus saves people a lot of time? Just a thought.