Every single computer interface would be copyrighted
Well, the original source files would be, if the API were published in the form of source code. You could still do a clean-room reimplementation, or choose one of the many that are freely licenced. Or write your own. The APIs that are locked up get ignored. Or, like the Win32 API, flourish anyway.
Or if you're Google, you could buy a license.
I agree copyright terms are far too long (thanks, Disney!), but I don't think that affects the principles at stake here.