Why is there a huge difference between flight time calculated by http://www.scoutuav.com/2011/05/12/calculate-flight-time/ and that by ecalc ?

The same rig shows a difference of about 25 min

There are no real parameters in that calculator. It is just battery discharge time calculator. However if you were able to put those values correctly for your quad then it will give correct output but its difficult to find avg amp draw as

1. It varies for every rig as it depends on motor and
2. Every flight is different as it depends on wind speed and temperature.
3. Aggressiveness while flying it.
4. Your ESC may not convert efficiently.
5. Your motor friction may be different.