Ethanol content; no clear data. However, Ethanol takes x3 the liquid volume per horsepower than 'gasoline'. So if you have 10% ethanol content, that instantly removes 3% of your horsepower; that then is also dependent on your engine- if it's carbureted, it can't adjust for the ethanol's additional oxygen requirement, and the engine runs lean, reducing power. This is the chainsaw scenario. On an EFI engine with oxygen sensors, the fuel system can increase the amount of liquid mixed in to maintain power, but then increases volume consumption. Either way, it sucks. But it doesn't explain the huge difference in mileage in the same vehicle of either type, with the same usage, using what is expected to be similar 'mandated' pump fuels.
We're being skinned, simple as.