If you've really forgotten all your basic atmospheric physics, let me remind you that there's a huge difference in the pressure differential between FL70-110 and the differential between FL310-350. Pressure lapse is not a constant rate, therefore the partial pressure of oxygen (which is fairly desirable for purposes of burning fuel) does not decay at a constant rate. It drops very rapidly at lower levels in the atmosphere, and then tails off exponentially.
Therefore your comparison with your 757 books is totally invalid.
I've just checked my ATR books.
At 21.5 tons, ISA, the burn at FL80 is 420 kg/eng/hr. That decreases by 10% at FL 120 to 383 kg/eng/hr, and by 26% to 312 kg/eng/hr at FL200.
If you think that an increase in fuel burn and consequently fuel costs of even a magnitude of 10% is insignificant, you have no idea at all about how small airlines' budgetting, finances and organisation works.
[ 20 October 2001: Message edited by: HugMonster ]