I stick with 25s for winter too. Especially if you're going to be mostly on roads that get salted / plowed semi-regularly. All of that slushy wet snow that builds up in intersections and road shoulders tends to gum up knobbies pretty quickly, while road tires shed the slop quickly and cut thru pretty well. As was mentioned, if youre on ice, your going to slip with anything other than studded tires.
If you've got a little bit of extra cash, its kinda nice to have a cheap conversion or something for the worst of winter as the elements tend to take their toll pretty quickly on frames and components.