Another key point (in my view) is that these APIs are textual whereas BIOS / protocols / binary interfaces are purely functional. Copyright is meant to cover "forms of expression". Text can have "expressive" creativity, but binary interfaces can have only functional creativity, which is expressly the realm of patents.
Of course, the only reason code is copyright-protected is because it's text, and text can have expressivity and code can be creative. But that does not mean code has creative expression. Most code does not express anything, not in the way other artworks do -- most code exists only to solve specific problems and hence is functional. Sure we can use whatever names we want for the methods and variables but you'll notice they all tend to be very descriptive of what they do. Not much creativity in the text of the code itself (at least for "good" code). All the creativity in software is in the technical ideas, approaches, algorithms and abstractions we use to solve those problems, but unfortunately only patents protect that, if at all.
The real problem here is the use of copyright to protect code. It's a legal hack, enacted because there was nothing better around to use. And to make the hack uglier, binaries enjoy copyright protection because they are "derivative works" from copyright-eligible program code. We need something more appropriate, lying between patents and copyright to protect software.
IIRC, it was some bytes of object code they copied to be interoperable, so that string could just as well have been an array of random numbers as far as being the key to interoperability was concerned.
Of course, the only reason code is copyright-protected is because it's text, and text can have expressivity and code can be creative. But that does not mean code has creative expression. Most code does not express anything, not in the way other artworks do -- most code exists only to solve specific problems and hence is functional. Sure we can use whatever names we want for the methods and variables but you'll notice they all tend to be very descriptive of what they do. Not much creativity in the text of the code itself (at least for "good" code). All the creativity in software is in the technical ideas, approaches, algorithms and abstractions we use to solve those problems, but unfortunately only patents protect that, if at all.
The real problem here is the use of copyright to protect code. It's a legal hack, enacted because there was nothing better around to use. And to make the hack uglier, binaries enjoy copyright protection because they are "derivative works" from copyright-eligible program code. We need something more appropriate, lying between patents and copyright to protect software.