how bad is the snow and ice where you are? I have not had any issues with my regular drivetrain but I have had issues with rim brakes in extremely cold temps where there are puddles that have not frozen yet. The rims can ice up and take a few revolutions of the wheel for the brakes to knock it off and start working. Disc brakes also solve the issue of rim wear if your city puts down a lot of abrasive stuff when it snows.
So basically I like both options but I would not deem either one a necessity. Having a back up commuter is always nice though, even for summer time. You can keep one bike ready for nasty weather with fenders on at all times and the other without them for a lighter bike that can be more of a play bike as well as a quicker commuter.