There's a lot of slack with crew and equipment, it's just when everyone gets out of place, the real debacle begins. My guess is that DL is being extra cautious and just bagging the flights before they have a real mess on their hands. Either way, they'll never please everyone. If they don't cancel and people get stuck on planes for unrealistic amounts of time, people will complain. If they cancel and the weather turns out to not be as bad, people will complain.