The pound-and-a-half weight of a current iPad sheds the tremendous amount of weight that would normally be needed for a conventional in-flight entertainment system built into the headrest, which on a typical 375-seat 767 could see the iPads pay for themselves within years, if not sooner.
ENGADGET: Qantas to hand out free iPads to all passengers on Boeing 767s, save fuel and our sanity (video)