I can't believe that is the reason. Not that I don't believe that is a leftie fear. MSM sources love sensational stories and this is a MUSLIM-CONNECTED SUICIDE BOMB IN AMERICA. It doesn't make sense that all government and 99% of media sources are on the same page that this should be hushed up out of PC fears.
More likely is that the MSM were ordered to keep a tight lid on this story. Why?
Videos of bodies hitting the pavement were shown all over the world, except here. The MSM is, like Janet Reno, more afraid of American religious cults and right wing wacko's than terrorists. I agree with SauronOfMordor that a movement could easily spring up. However, it will not be a rebirth of the KKK, because that group has a lot of emotional ties to Arabs through Nazi sympathies.