For all the bad press it received, I believe that Carmageddon only contains fantasy violence. No car on Earth could take so much damage in real life without blowing up or instantly killing the driver. Postal and GTA cross the boundary into realistic violence. People do go 'postal' and go on killing sprees for unknown or stupid reasons. The two little boys in Arkansas are perfect examples.
People do get car-jacked and killed.
Policemen do get severely hurt or killed trying to protect people. Civilians do get caught in the crossfire. I tend to think that this is horrible, both for those of us in the US and for the rest of the world. The same goes for violent and disturbing content in the media. My understanding is that the US is seen as a childish, lawless, and violent society overseas.