I'm in Philly and we get a fair amount of snow (although not at the levels of WI). I considered keeping my Blazer as a winter car but I just can't afford two cars. Look at this way, it's only a few months out of the year. Now think about how many days of those months there is actually snow ON THE ROAD. Around here, the snow is cleared within a day. So that means you can't drive on the day the snow hits the ground. But then again, not many other cars can. Mustangs seem to have a reputation that they, and only they, are horrible in bad weather (rain or snow). I've never owned a FWD car, and as long as you know how to handle the vehicle and respect the car's limitations, you'll be fine.
I've driven my Blazer in the snow with the 4x4 turned off, just to see how it would handle. Yes, it gets a little slippery, but nothing major. My girlfriend's front drive Toyota had similar slips (obviously the slips were different since power was to teh front of the car, but you get the idea). Unless you're cmparing the Mustang to a true off-road vehicle, it'll handle just as well as any other car on the road