I think the "always Winter, never Christmas" thing is, in part, a way of saying that it's not the winter in-and-of-itself that's the problem: it's the unnatural winter. Winter is supposed to have a cycle: you have winter and the winter dances (I'm thinking here of the Silver Chair, when Eustace and Jill climb out into one of the fauns' celebrations) and all that stuff, but THEN, you have Christmas and winter starts its long slide into Spring, and so on. (I also seasonally associate the Pevensies [Lucy for Spring, Susan for Summer, Peter for Autumn and Edmund for Winter] for various reasons, but I am a gigantic dork.)

I may very well have spent way, way too much time thinking about this, for serious.