This is not an answer, but I will post it in the hope that it may resolve some of your confusions.  I am afraid that you seem to be mixing “shorter” in the sense that it uses less _characters_ and “shorter” in the sense that it uses less _area_ in typical typesetting (hence less pages in typical books, assuming that the size of a page is similar in books in English and books in Japanese).

I think that it is fair to say that text in Japanese tends to use less characters than the corresponding text in English, because the writing system of Japanese has more characters to choose from.  However, for the same reason, characters in Japanese are more complicated in those in English, and therefore characters in Japanese are printed in a larger size in books than those in English.  Therefore, it would not be surprising if books in Japanese sometimes have more pages than the corresponding books in English.

By the way, I realized that you used several novels to compare the number of pages of books in English and Japanese (from your comment):

> I already did something on my own, comparing Anna Karenina, Crime and Punishment and Catcher in the Rye in Japanese and English (using Amazon book data).  Interesting enough, the Japanese version of The Catcher in the Rye had more pages than the English one.

I think that it is understandable if translation makes text longer, especially in case of novels.  A novel in some language is usually written in such a way that it is natural in that language.  Translation tries to mimic what is stated in the original text in another language, which forces less natural way of using the language.  Of course “natural” does not have to mean “short,” but I think that it is plausible to assume that translation may have some implication on the length of text.  I would try to see if the comparison gives the opposite results in case of novels originally written in Japanese and their translations into English.