[blywi]

I think the answer is in the article text "all meticulously sectioned by publisher". Book sizes differ somewhat between publishers, but each publisher tends to only print books in a few standard sizes. For the paperback editions this is even more reduced, it usually looks to me like all paperbacks from one publisher are the same size.

[kwanbix]

I never undertood why publishers couldn't agree in 5 different sizes or so.

[sinuhe69]

Because they are an industry, aren’t they? Printing, binding, cover productions, transportation and storage, all that are much easier and much cheaper with a few standardized sizes.

[kwanbix]

That is exactly what I said.

[pseudohadamard]

They're German publishers, they probably all adhere strictly to DIN sizing.