I don't know about the flat question. I never got a flat on that bike, but then, I commuted in DC for four years without a flat on my regular commuting bike. I always make sure my tires are properly inflated, which I think helps tremendously in preventing flats.

Fenders do keep you and the bike cleaner, but you need to check them constantly. At least, I did. I had a situation where the fender got loose while I was riding and it worked it way down so that the tire actually rode over it. Hard to explain, but it stopped the bike in its tracks and knocked me to the ground. After that, I just took the darn things off.

How far is your commute? Mine was 14 miles each way, and I rode into the 20F temperature range, but if it got into the teens, I'd find another solution. Sometimes that didn't work, though, as one morning when it was 9F I decided to drive rather than wait for the bus in that cold, and one mile into the drive my car stopped working because the radiator was frozen. Or something like that--I'm not a mechanic. That was unpleasant, and I would have been better off riding my bike and moving, or even better just calling in sick!

Nokian makes studded tires for all size wheels. Cross bike should not be a problem. They are not cheap, but if you plan on riding where there is ice, it might be worth it to you. It's certainly worth it to me to avoid going down on black ice.

I really like riding in the ice and snow. I have since sold that Dahon, but I do still have the studded tires. I have an old mountain bike that I might put them on for this winter. I no longer commute to work since I work from home, but it would be fun to go out and ride in the snow and ice this winter. We had alot last winter, but it's not consistent here.