They're open on Boxing Day, as stated in the post. It's only usually businesses run by people that don't celebrate Christmas that are open (like Chinese restaurants, and that one gas station run by a Pakistani family in my old rural town that saved my hide in 2012 by being open after I forgot to get gas on Christmas Eve).
Most movie theaters are open Christmas Day in the US as well, not just boxing day. I've been to quite a few movies on the 25th. Tons of major films are released Christmas Day because it's such a high grossing day in the industry