Same type of plane, same fuel, same distance - so how is it that the run from JFK to LAX that used to take six hours now runs close to seven hours? It has to do with padding the scheduled durations so that late flights officially arrive "on-time" and planes are better able to pull into gates on schedule. For passengers, of course, all it means is an extra hour of travel time - often sitting and waiting. From WSJ's Scott McCartney:
For some airlines, longer scheduled times for flights reflects the reality of inefficiency in the nation's air travel system, which often can't handle the volume of planes without delay, especially when bad weather hits. For others, lengthening scheduled arrival times boosts on-time rankings charted by the Department of Transportation: Those numbers can have a real effect on public perception. And in some cases, block times have grown simply because airlines have been making so many schedule changes as they have reduced capacity over the past two years. Flights that took off without a wait can now end up stuck waiting behind a line of jets because departure times have been changed.
Other examples of inflated travel times (percentage increase from 1996)
Phoenix-Las Vegas (Southwest) 1:20 +33%
Los Angeles-San Francisco (United) 1:36 +19 25%
New York JFK-Los Angeles (Delta) 7:04 +18%
Portland, Ore.-Los Angeles (Alaska) 2:22 +10