I haven't checked the international recommendations and guidelines, but my understanding is that those are extremely over-cautious. I guess the Japanese gov is following those guidelines by the letter.

Extremely over-cautious is a good thing. With huge populations, a very small increase in the probability of developing cancer will translate into a number of real people getting seriously ill (though curable, in most circumstances).

Sheep and raindeer grazing in certain mountain areas of Scandinavia are still monitored for radiation levels after Chernobyl. You would have to eat A LOT of meat, and the risk would still not register on the "ridiculously low" part of the scale. Yet, some of these animals will have to be put on special diets for a few weeks to get certain materials out of their system before they can become food for humans.

The most important issue is that you DO NOT want to have any doubt what so ever about food safety and radiation levels. Strict is good.