The reason I take things literally is probably attributed to the fact that I have Asperger's Syndrome (look it up if you're interested).
I agree with you when you say you don't need extreme cold for a battleground snowfall - in fact it preferably needs to be warmer for obvious reasons! I also agree with you about the wintry element of Spring and whatnot, in fact I strongly agree!
But really, for me in the Midlands, any lying snow or really anything more than a few wintry showers is rather unusual before Christmas, and particularly so before mid-month (as I said it's probably a different story for you in Scotland). I suppose that makes December 2010 all the more exceptional! IMO and for my area the first half of March has more potential (probably not exceptionally so though) than early December. So with that mind I consider Winter as mid-December to mid-March. Although as I said, it's just my opinion!!!!
The reason I started this topic was because I have seen posts in this forum which say things like "I often consider X part of X month to be X season", so I became curious!