I would say most modern code is not the kind of code written with the absurd platform assumptions that old code used to do. There's not magic addresses you have to know to talk to hardware, there's no implicit memory segmentation/memory looping, and so on. Ever since most modern OSs try to prevent direct access or randomize address spaces and so on it just is hard to write code that is insane like the way we were.

So the question is are you contesting the POSIX defined behaviour over using more logical interfaces from the OS or the wild west where people were hacking around broken, platform-specific features and often broken or awkward system libraries or just the more modern case where people use the standard interface instead of a more performant one. In the latter case I agree I wish there was a more 'nice' way of doing more dynamic and efficient feature detection without making simple C programs crazy complex.