This is a story of conservation and content. The story is in the refineries.
The gas you use in winter is different from what you use in summer. It's different depending on where you live.
Gas used in the winter contains a lot of butane. Butane is cheap, but it turns to gas at about the melting point of water. That's why your gas cap has a “vapor lock” – it's trying to trap the gases in the gas in the tank, so they can be used, rather than blow away and be wasted.
What replaces butane in summer gas? Mainly ethanol. Alcohol. It can be made in the refining process, or it can be made in other ways. Ethanol costs more than butane. Some people pay as much as $250/gallon for it – if it's properly aged in the right barrels. But even the cheapest ethanol has a price higher than that of butane.