[KyleGoetz]

I wonder if it's because Japanese notates with . base-1000 but notes with kanji base-10000.

In other words, you put a . every three digits, but a new kanji comes into play every four.

1.000 man = 1.000 x 10.000 = 100.000.000
So in one, it's a "thousand" or something, but the other it's a "hundred" of something.

What I mean is that every three digits you have a dot, but every four digits you'd have man, oku, chou, etc.

Whereas in many western languages, you have them in harmony. Every three digits is a ., and every three digits you introduce thousand, million, billion, trillion, etc.

I think people struggle in English only past 100 billion, and that's only because almost never do you even have to use the word "trillion."