How much truth is coming out of Japan?
Loss of face could be a factor in how much is being reported. Its a possibility and something to consider.
Another one to consider is that ultimately the airline wouldn't give a damn if there was a radiation risk. All they want is bums on seats and ops normal.
Had it been a volcanic ash issue it may be different. Thats a threat to the machinery and thats a different story entirely.
Sorry guys I've got my cynical hat on today.