I don't see it as an issue of being PC. There's so much subliminal advertising that goes on and getting away from that for this one movie is not a bad idea. I'm not aware that there was any kind of public outcry about Han having a gun in the poster. What I hope happened is an executive saying that "in this time of proliferating school shootings, it looks bad on our part to throw another poster of our hero holding a gun to help sell our movie, so let's change it."
maybe it's the optimist in me hoping so. Maybe it's the pessimist in others seeing something nefarious. Whatever it is, I applaud them for making the change.