This makes sense if you view "1.7" as encompassing all of the releases

1.7.0, 1.7.1, 1.7.2, etc. (and their variants). It's a bit like the
"significant digits" of a number. [1] You want the release to be
bigger than all releases of that type.

but is this really the underlying concept?
Does the PEP explain this as a justification? Where?