Quote: "Colder weather coincides with winter-blend gasoline that results in lower gas mileage across the board."
Actually, there is generally an effort to lessen the amount of Ethanol in gas consumed through winter months. This is because Ethanol has an unfortunate tendency to attract water. See this video for more info:
If you want to know more, you can also read this article on the subject:
Unfortunately, US refineries utilize MTBE as an additive, although it has been proven that this particular additive is commonly the cause of cancers.
Using the automatic settings on your Jeep heater and cooler allows for the A/C unit to run, which decreases gas mileage as Rednecktruck correctly argued.
It is also true that cold starts have a negative impact on gas mileage. However, depending on the distance travelled when driving your car after a cold start may both cause a minimal or a significant impact on your general consumption of gas. Long trips will outweight this tendency, but short trips may amplify the effect.
Hope this helps!