Energy isn't everything - the rate at which you're able to access that energy is power, and usually folks are after power.

Alcohol fuels have lower specific energy content (Btu/lb), but they run so much more fuel per unit of air (5:1 vs. 15:1 for gasoline) that they wind up producing about 20% more power, all else being equal. See SmokemUp, for example. I like his summary - "Gasoline is for washing parts, alcohol is for drinking and nitro is for racing."