I have written an extensive blog post on this question in April: http://www.mobilecrunch.com/2010…
Basically, what people in Japan and elsewhere define as a smartphone is vastly different. In the US, for example, it’s a phone with advanced functionality, for example web browsing capability.
In Japan however, even the simplest models let you browse the web and have an array of flashy functions. That’s why in Japan, some people basically place phones with OS not made by local makers, for example the iPhone, Blackberry, HTC phones etc., in the smartphone segment.
And it’s in this specific and narrowed down segment that the iPhone captured 72% market share. Another explanation is that at the time of the survey, there were not even five different Android phones on the Japanese market (the situation for Android is gradually getting better).
But just like anywhere else, there is no valid and universally adopted definition of what the term smartphone really means so the survey is not to be taken too seriously.