It makes perfect sense when you think about who the audience for this data is, economists, planners etc. In those roles, the primary concern is the actual quantity of heat and electricity that the population needs in their homes and workplaces, and you need to be able to back that out to how much raw fuel that requires, or how much transmission capacity you need. You need to know this summary info so you know where the focus needs to be. At moment for instance, they need to know how much gas they need in storage tanks in Europe for this winter, and it's information like this that helps them figure that out.