Irene just last year, was estimated to cost over 15 Billion and millions were without power. So Sandy was not unique because we had almost the exact situation just last year with respect to damage and power loss. What was unique was the combining of the two storms. Just pointing out that the hysteria about Sandy is just that, hysteria. The damage is bad, but not unprecedented.
Hurricane Irene one year later: Storm cost $15.8
First of all, you can pretty much take initial damage estimates and double them. Second, Sandy was a hurricane until just before landfall. I watched the sat photos and microwave passes, it developed a distinct eye Monday. And that in turn, IMO, changed the nature of the storm when it hit land. It was expected to be transitioned to an extratropical storm a day before landfall, which means the higher winds aloft would be brought down to the ground and the storm would be strengthened by baroclinic processes, and we would have seen a lot more power outages further inland. I don't think that happened much, the landfall progression of winds were much more typical of a tropical system and by the time the worst of the storm reached where I am, in NW Montgomery County in PA, the winds were not that bad. And third, the damage was very different between Irene and Sandy. Irene was mainly an inland flooding event. Sandy was a coastal flooding event - because it apporoached the coast head-on instead of with a glancing blow. The real wildcard for damage estimates is going to be how much repair the subway system will need because of saltwater immersion. They just don't know, but I saw a report that estimated it would take $55 billion to fix the system if it flooded. Now, that would probably be the entire system, but I think it's a good change that the subway system damage will add a fair chunk to the final damage bill.
So in a way, they got part of the forecast wrong. Baroclinic factors did not juice up the storm the amount they envisioned. But it was a tropical system and a hurricane up until just before landfall.