My personal thoughts of what a "winter bike" is, is simply the one you own that you don't mind if if it gets corroded or a bit messed up. My Trek has mudguards and all that, and also a few rusty bits, it's not very pretty.
Maybe I am anally obsessive as defined by
@r04DiE , but if the weather's bad, and it's winter, (and I have to ride), it's the heavy old Trek that I'm taking out. My road bike is for fair weather, it cost me quite a lot of money, and I'm not apologetic about wanting to keep it out of the salt and the spray.