The scheduled time (door closed to door opened) of a flight between 2 airports is based on
- time on the ground from the door closed to ready for take off. For some airports this can be a lot of time.
- take-off and climb to altitude.
- the cruise at altitude. Now days the speed of aircraft does not change much from minimum to maximum. And ground speed is airspeed plus/minus winds. The prevailing wind in some places can be a lot.
- the route is not always a straight line between airports. There are "highways in the air". And politics can influence a route.
- decent from altitude to the airport landing.
- time on the ground from touch down to the door opened. For some airports this can be a lot of time.
- some airlines add padding for air traffic delays, weather, ground delays.
The time flying at altitude is only a portion of the total time..
http://www.gcmap.com/mapui?P=TPE-PEK+&DU=mi&SU=kts&RS=best
You do not always earn 1 frequent flyer mile for 1 mile of distance. Now not unusable to earn 25%, 50%, 75% or what ever
http://www.wheretocredit.com/air-china