It is neither "the impending class war/riots" (do you really believe that nonsense?) nor "the economy causing this." It is a function of the fact that many gun enthusiasts believe, despite no evidence to the contrary, that President Obama will take some action to limit gun rights. Despite President Obama doing no such thing at any time, the underlying idea seems to be that as a lame-duck President in a second term he might change his course.
This is strictly an emotional reaction, in that a) President Obama has never demonstrated any inclination he might actually try to limit gun rights; and b) there is no way any gun control measure would make it through our current Congress. That being said, it's a good way for the NRA and the gun industry to get people whipped up, and thus infuse money into the gun industry in an economy which has left many American strapped for disposable income. I find it curious that people act so emotionally, en masse, for no clear reason, but that's human nature.