Please watch that first video, it's a good one. It explains how CPython essentially _is_ the spec because its internals leak into the spec when they have no business being there.
Pretty much the same is true about most other languages that have a single main implementation. This is even true, to some degree, for Java, which had competing implementations relatively early on.
At some point it leaked pretty hard as well. The package scope was an unspecced implementation behaviour that became a standard later. (If I recall the story correctly)
