This strikes me as political.
It might indeed be political but it is also definately economic. Many items that are assembled in China have raw materials/subassemblies that are made in Japan. If China is turning down raw materials from Japan because of radiation then they have an alterior motive for doing so.
In January, China was experiencing inflation and wanted to pass on higher prices to importers. In most cases the importers balked and Japan decided to "slow down" their production rate. They figured that the same amount of money chasing fewer goods would mean they could pass on higher prices to the importers. Now it looks like theearthquake/tsunami/nuclear crisis has given them another excuse to slow down their production rate. If I were a betting man I would bet that by early summer we will be paying significantly higher prices for fewer goods assembled in China...even though the earthquake/tsunami happened in Japan.