At the risk of gross oversimplification, here are a few differences:
1) Corporate Blogs: in the US, I suspect lawyers and marketing departments have huge influence, leading to a somewhat sanitary feel from most company blogs (even internal ones). In Japan, where there are far fewer lawyers, corporations are often much more interested in creating a sense of small-town community, which lends itself to a gentler, somewhat more natural, feel.
2) Cute: in Japan cute is good. The cuter the better. Even for guys. Blogs need to be cute.
3) Community: Japan is big on the group, and creating membership around common interests. The US is big on individualism. Japan is also big on hobbies. "What is your hobby?" is far more common conversational starter than it would ever be in the US.
4) Harmony: many US bloggers revel in their role challenging the main stream media and powerful interests (governments and corporations among them). Japan tends to favor harmony, and there is far less challenging of authority. When it does happen, it tends to be far more subtle.
That's just for starters. . .I'm sure books could be written on this!
