Theatre owners are well aware of threats to their business, and the resulting litigation should there be one of the so called "lone wolf attacks". Besides that, if there were no threat, why would they need an "out"? Fear of selling tickets?
Fear of not selling tickets.
Theater chains rarely see any meaningful money from tickets sold, and often see none; the bulk of their profits come from concession stand sales.
Film distributors like Sony Pictures are in the power seat, leveraging theater chains to screen movies the chains don't want in order to also screen films likely to get big draws and lead to more popcorn, candy and soda sales.
Early word at Sony was the finished product was weak; between costs to make and market, traditional iffy performance of political satires, the expectation that the movie wouldn't make much money internationally and projections that domestically it would barely break even, and, finally, mixed early reviews, Sony was a bit over a barrel with this one even before the terrorism element emerged.
The real threat was everyone was going to take a bath. If Sony had a product they had financial faith in, they could've shoved it down the theater chains' throats. They didn't, and gave the chains an out based on "threat" but that financially benefitted all.
If all other elements were the same, but this was a Spielberg extravaganza, Sony, the theater chains and all involved would make a "prinicpled" stand against terrorism and let dumptrucks of cash calm their nerves.
I've seen that Homeland Security press release too. I don't give it it credibility. When they say they don't perceive a threat, it means they got caught sleeping.
Like any other agency, DHS gets it right sometimes and gets it wrong others; I'm not so quick to automatically assume that failure to perceive a threat de facto means incompetence on their part.
But I wasn't referencing their assessment; hardcore NK watchers who see NK's fingerprints here largely agree that, like the attack itself, the threat of theater attacks was purely virtual, designed to further intimidate and nothing more. A digital attack of this kind may or may not ultimately provoke U.S. (and other) retaliation (the current administration is clearly floating trial balloons in the media to see if non-retialiation -- apparently preferred by them -- is politically viable), but physical attacks would guarantee significant retaliation of a kind and scale the perpetrators of this cyberattack appear -- based on the limited nature of the attack -- do not want, and NK certainly would not want if they're partly or wholly responsible.