It is my hunch that pax are now understanding that the listed 'Departure Time' is 'Time To Be Onboard'! Whilst all carriers now build in large amounts of 'padding' to their schedules, they also make a real show of arrival times. (Some more than others ..)
I certainly agree with +TSRA that customers are all too ready to consider the supplier (not just airlines but ALL companies) as incompetent and the availability of 'electronic lynching' can only be met by the carrier being on the ball to respond online to those twit messages. However, to do that requires more staff and, ever since money was invented, people have shown that they want to spend as little as possible to get the maximum.
Which is why I think this is more of a transitory problem. New generations of pax are learning this from Day One, the older pax have to re-learn what they understood of airline timetables being like railway timetables. New generations growing up with the LCC 'everything is an optional extra' understand better and will, I trust, be more understanding. Meanwhile, the ground and air crews have to put up with the ill informed and those quick to judge.