The bits and pieces mostly jibe with what we've been seeing and hearing in the media since the DPJ took over. That's what's remarkable about the US wikileaks in general. It's like, tell me something we hadn't known or suspected. That said:
..."Compartmentalization and risk aversion within the bureaucracy, however, could increase Japan's vulnerability to threats for which it is less prepared,"Note that the first sentence appears to refer to the response to a threat for which it has not prepared for, while the subsequent paragraph appears to be referring to the lack of preparedness itself. These are two connected but logically distinct propositions. Confuse the two, and you get a narrative that is literally nonsense. A bureaucracy, of course, is by nature compartmentalized and risk-averse, so, left to its own resources, will always respond poorly to the unforeseen. Case in point: Hurricane Katrina. That is why leadership is so important. Case in point: Hurricane Katrina. And leadership is where the Japanese public is pinning the blame on. In my conversations on this subject, I've insisted that the typical response under the LDP regime to a nuclear disaster--any disaster--would have been to put the administrative deputy chief cabinet secretary in charge of crack bureaucrats assembled from the responsible ministries, team him up with a parliamentary DCCS, and have chief cabinet secretary preside over the entire process. The CCS could share the chores of public communications with the prime minister. Basically, put the people who know how the parts work, to minimize on-the-job learning. Instead, Kan approached the task as if a car broke down in the middle of the road, tried to repair it himself, then ignored the manual and started asking passers-by for advice.
Bureaucratic decision making has been cited as a factor in Japan's lack of preparedness, almost exactly three years later, for the record-breaking tsunami that crippled the Fukushima Daiichi Nuclear Power Station and set off the worst nuclear disaster since Chernobyl. While the cable offers few specifics about the weaknesses in Japan's disaster planning, it does go on to warn that a blow that disables the country could have catastrophic consequences for global trade and finance.
That said, I suspect that most of the things that came to pass were driven by science and engineering and that most of the mistakes came in the public communications process. Note, though, that the human response to any nuclear disaster tends to be deeply irrational, unscientific, and apocalyptic. This means that the margin of error for managing the figurative—if not the physical—fallout is very small compared to other disasters, such as massive toxic chemical spills—or the tsunami itself.