Without wishing to appear as if im taking sides here, i'd just like to point out that magazine/internet figures rarely ever give an accurate view of how a vehicle is gonna perform economy wise. For example, online and magazine sources state that the average Fuel consumption figures for the Jeep Grand Cherokee 4.7 stand at around 20MPG which equates to 8.3 KMp/l.... however, real world, it does about 3.5Kml in town maximum....
therefore logic states that the hummer, which has something like 1.3 more liters in engine capacity, and is about as aerodynamic as a garden shed (not to mention approaching 3 tons in weight) is going to be significantly worse when it comes to consumption..... so 2.4 Km/l aint far off