Books are not equivalent to software because software has a functional purpose. While programming has creative elements, the primary goal of a program is to achieve certain functions (whereas the primary goal of a book is to enable creative expression or to record factual information).

If I want to support a Windows program on Linux I have no choice but to implement the Windows API. Likewise, if I want to interface with a program that stores data in S3, I have to replicate the S3 API.

That's why I think that there's no good analogy for software APIs among traditional media.

As far as the law goes, Google's argument is that because software APIs are arbitrary choices and necessary to be copied for interoperability that software APIs are noncopyrightable under section (b) of this statute. https://www.law.cornell.edu/uscode/text/17/102