The loss in fuel economy in the winter in not completely due to oxygenates in fuels. In colder weather, air has a higher density, and to get the correct mixture, more fuel is added to the airstream, if that airstream warms up after starting from the EGR system the fuel system has to adapt, not something that changes instantly. On older cars, you just adjusted the carb to run rich to offset the cooler air. On our new trucks the computer adjusts the fuel rate to match the input value on the mass airflow sensor.

So poor mileage in cold weather is due to a number of factors the least of them being oxygenated fuel.

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2000 F150 SC SB 4x4 XLT
Trition 4.6, 5 sp manual, Factory class III tow package, sliding rear window,
3.55 LS pumpkins, P255 70R16 slippery when wet Goodyear RT/S, WMY1 Superchip!!!

Mods: Lund Deflecta-shield II, K & N filtercharger, Gibson 3" side swept cat back exhaust