Can't answer your first question other than to say that if I were looking at a new commuting bike, I'd probably seriously consider a cyclocross bike next time. I am a year round commuter and ride in all conditions. In answer to your question about road tires for snow/icy conditions, I think you have to look at studded tires (see the Winter Cycling forums for discussions). But, one important thing to note is that there are no narrow studded tires and your bike has to be able to take a 32 or 35 mm wide tire. That's another good reason for a cyclocross bike. I have Schwalbe Winter Marathon studded tires that I use on an old rigid MTB with 26" wheels once the temperatures regularly drop below freezing. see http://www.peterwhitecycles.com/studdedtires.asp for a good discussion of studded tires.