JTNY, agreed with you there, winter MPG suffers all around due to colder weather, additives in the fuel, snow tires for some and depending on the driver possibly idling prior to driving. In the vehicles I've owned (this is #12, omg, hahaha) I generally have come to expect a 10% drop off in mpg during the winter months.
It also appears that buyers of the new impreza are generally in the northern areas (not surprising since the advertised mpg coupled w/AWD are unheard of), so everyone is starting off in colder climates. With a car that gets such high MPG a 10%+ dip costs potentiall 3-5mpg, which is more pronounced over a car that starts with worse overall MPG ratings. We'll start seeing the true potential when our cars are more broken in, and the weather warms up.