The negligible risk we can not ignore

After the nuclear accident in Japan provides many experts soothing descriptions of possible consequences. A meltdown does not mean disaster, and a bit elevated radiation risk means reminding a public health threat than the release of the sofa with a bag of chips. The picture does not seem to go together with the one of the world's largest nuclear accident is underway.
How is it that the descriptions of the threats and risks can vary so much? 

Logically and statistically is more likely to get in trouble if you drive a car than if you live near a nuclear plant. Yet we would never be willing to accept the same risk awareness in the handling of radioactivity when driving.
We seem to have very different ways of looking at risks, but why is it so?