To be more precise...
if NIT is capable of working 3h from 1500mAh battery - that means with mean value of voltage equal to 3.6V - gives us 1.8W of energy - for the WHOLE SYSTEM.
Forget ANY chip alone.
Go and lite up the screen and 2 mmc card reads/writes with that power.
And since I've got some background as low power - battery powered devices HW designer IMHO it's well designed.
Of course - probably one could make it more efficient but believe me - it wouldn't be "just like that" with today's technology.