The workforce for a lot of industrial things has been more centralized in the North previously resulting in it being where many firearm companies put their factories. You already had a large workforced trained to do the type of things required.
There is also politically some benefit to having jobs dependent on firearm manufacture in states that are less supportive, they are less likely to be as anti gun if big local dollars and part of the economy is tied to firearms, as well as historical and traiditional companies dating back as far as many once did there.
But yes now the south is the better place for wage slaves, right to work states where Unions have not established benefit requirements for industrial positions. Plus friendlier to the product, I do see most new industrial companies being located in the South.
Of course large industry does come with its own price, the NE has had pollution problems as well, in many cases covered up until the cancer rates of some areas went through the roof and it turned out the local industry wasn't following the law and industrial chemicals were in the local water table or enviornment. It also has the biggest issue with acid rain destroying forests (swamps in the south would be even more vulnerable) although part of that is the weather patterns bringing the air from much of the country trhough the Northeast.
Just take a look at some of the biggest current acknowledged problems:
http://toxmap.nlm.nih.gov/toxmap/superfund/navigate.do
The Sun Belt being a bit more naive to such things and will let business operate more freely, I see a lot of those issues repeating themselves.
As for Sandy, it is really a demonstration of how vulnerable the infrastructure is in a place they do not expect storms. Sandy was in fact far more mild than what Florida and to a lesser extent the Gulf deals with almost every year. New York and Jersey just don't get thier underbuilt structures destroyed very often so had a lot more whose time came from something that was barely a category 1 and quickly fizzled to much less.