Thanks for the replies, those we're some detailed responses
As for the questions regarding the two people I mentioned. They usually turn their car on and let it sit for 1-2 minutes, then drive. Both of the cars yielded their 'EPA numbers' when driven on the highway for longer drives, so I was more inclined to say it was their short trip, not the car. The Accord is auto, and is driven easy, the C300 is stick and the driver usually leaves it in a high gear with the rpms low, granted it's not bogging the engine. As for where they drive it's mostly residential, with maybe 1-2 traffic lights/stop signs on their whole ride.
I'm little confused with the cold air in the winter. How exactly does the air 'warm' up in the winter time after driving? Is this where the blowback from the PCV system play a role and recycle warm blowback? Or does the heat from the engine bay itself 'warm' up the air that is being drawn in, or is it both? I know on my father's old carburetor'd corolla their is a heat pipe running from his intake manifold to the front of his air intake duct. I remember someone from an auto store was telling me it's to warm up the air in the winter, I guess the same theory would apply to above?