One reason is language. It's possible to say so much more in Japanese within Twitter's 140 letter limit. The word "information" requires just two letters in Japanese. That allows academics and politicians to relay complex views, according to Tsuda, who believes Twitter could easily attract 20 million people in Japan soon.
Another is that people are owning up to their identities on Twitter. Anonymity tended to be the rule on popular Japanese Web sites, and horror stories abounded about people getting targeted in smear-campaigns that were launched under the shroud of anonymity.
In contrast, Twitter anecdotes are heartwarming. One well-known case is a woman who posted on Twitter the photo of a park her father sent in an e-mail attachment before he died. Twitter was immediately abuzz with people comparing parks.
I look forward to future comparative studies on how citizens in different countries use Twitter. I'm also taken by the translation of "tweet" as "mumble." For me, there's a humility and a demureness there that isn't very present in much of American tweeting, particularly by 'social media experts.'