orthography - Is there a reason why numbers in Japanese are delimited into blocks of four?

As I understand, Japanese numbers are divided into blocks of four, so while we would think of the number 89123889 as 89,123,889, in Japan they would think of it as 8912,3889 (八千九百十二万三千八百八十九). So English uses thousands and Japanese uses tens of thousands.

Is there any particular reason for this? Not that it matters either way, I'm just wondering at what point either culture chose to delimit numbers by thousands, or tens of thousands.

If you reply with Japanese, please use hiragana and furigana only, except for number kanji.

Answer

This is a summary of this Wikipedia article.

A math book called 塵劫記【じんこうき】 published in 1627, was the first book that described (and probably defined) how to count large numbers in Japanese.

In the first edition of the book, actually there was no "4-digit grouping" as we know today, at least for relatively small numbers (smaller than 1 極【ごく】). A different kanji was used for each digit. 10⁴ was 万, 10⁵ was 億, 10⁶ was 兆 ... and so on, until it reached 1 極, which was only(?) 10¹⁵.

Soon after that, the 4-digit grouping was introduced in a revised edition of 塵劫記 published in 1631, and 1 極 bacame 10⁴⁸. In this edition, 8-digit grouping was still used for numbers even larger than 1 極 (100000000 極 = 1 恒河沙【こうがしゃ】, 100000000 恒河沙 = 1 阿僧祇【あそうぎ】, and so on)

In a year 1634 edition, the 8-digit grouping was completely removed, and the simple 4-digit grouping system after 万(=10⁴) remained. This is exactly how Japanese count large numbers today.

Before 塵劫記, Japanese had relatively small vocabulary for big numbers, and 万【よろづ】 (=10⁴) seems to be the largest unit. 八百万【やおよろづ】 meant "countless."

This 4-digit loop is borrowed from Chinese numeric system. Korea also uses a similar system. However I couldn't find why and when Chinese started to use 4-digit scale instead of 3.

(By the way, I was surprised that English-speaking people used long (6-digit) scale until relatively recently.)