I’m German. If the pages are a comfortable size, why does no publisher ever use A5 or A4 paper? To quote an answer I gave to another comment here:
Let’s check. I grabbed four random German books from my bookshelf. If you’re right, the pages should either be roughly 30cm×21cm (A4) or 15cm×10.5cm (A5).
Book 1: 18cm × 11.5; book 2: 19cm×12.5cm; book 3: 20.5cm × 12.5cm; book 4: 24cm × 17cm. None of those conform to the standard.
Another hint that the paper format is weird is that scientific papers on A4 are always either printed in two columns or use the ninths rule for margins, i.e. 1/9 of margin on the inner and upper edges and 2/9 of margin on the outer and bottom edges, essentially throwing away almost half of the page (I’ll admit there are more economic recommendations of 1/11 or 1/13). This is to make the columns narrower to get closer to the target of 60–80 characters per line. Note also that this makes the ‘usable’ area approximately 20cm long, which is much closer to the American’s ‘Legal’ format (216mm).
You’re right. Sorry for getting my post-7pm arithmetic skills on you. However, my point still stands. ‘Close’ is not ‘conforming’ to the standard.