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A couple of blogs (below) give credit to Matsumoto (author of the Japanese blog):

http://obamapacman.com/2011/10/subtle-differences-of-ios-5-v...

http://usersillusions.com/post/11948201269/apple-has-made-so...

And here is a another site discussing the same images without any attribution.

http://www.ipad2iphone5.com/these-ios-5-changes-are-you-cert...

Probably because the number of people who can read English greatly outnumbers the number of people who can read Japanese?

It's very common for Japanese to use English labeled slides and diagrams for presentations that they know they will be taking abroad because it is much easier change the language of the explanatory text than it is to edit images to make them English.

Note that the locale of iOS in the screenshots is Japanese. The author has done a number of these types of examinations before, usually with parallel Japanese & English captioning.

Maybe credit notes are written in Japanese :)