The difference between 9-11 and WW2 is simple: 50 years, give or take. Time has a way of healing anything, even something as traumatic as, say, thousands of civillians dying because of terrorists doing such an awful thing, or from thousands of soldiers dying before they even get to shore on Omaha Beach. People don't make games even mentioning the twin towers because 9-11 is fairly recent... however, did you notice that, once your grandparents (the ones who participated in WW2 and can remember it personally) started dying off, a splurge of WW2 movies and games came out? The same shall happen with 9-11. There's a good chance you'll be alive to hear the first 9-11 joke that people will laugh at... and you will laugh at. Just give the scar time to heal over a bit.