The numbers are not adding up. Jetboil uses 8.33g of an isobutane/propane mix to boil one liter of water.
The Jetboil doesn't specify the temperature of the water when the test was started.
7.54/0.8 = 9.425 gms to boil one litre, the fuel physics table has the following note
In theory it takes about 0.38MJ to heat 1 litre of water from 10C to boiling, or 1.8kW to do this in 3.5 minutes. Real stoves need double this energy to allow for heating inefficiency. At full power this efficiency will drop as so much heat goes up the side of the pot and is wasted. This will also vary significantly depending on wind speed, wind shield, pot shape and size, initial water temperature, and use of a lid. Watching the pot is also rumoured to slow it down :-)
The heat exchanger pot systems have raised the overall stove efficiency from around 50% to around 80%.
So it may be that the difference of 9.425 - 8.33 gms = 1.09 gms is just the fact that Jetboil started their water temperature around 20C rather than 10C.
It really doesn't matter, its only for a ball park comparative analysis.
Remember though that the 3 to 1 ratio of alcohol to isobutane/propane mix per unit volume says nothing about the weight difference. The Jetboil + 500 gram gas cartridge will still be lighter than the alcohol setup which boils 30 Litres and will get you 50+ litres of boiling water.
If you are getting around 10-11 gms or less per real world litre boil using cartridge gas your doing pretty well.
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