i think you are right about the natural way to interpret the text - although if that was the intention it could probably be worded more clearly e.g. by adding 'renamed' or 'instead' or both.
My issue is that - at least as far as i can recall - the default superuser was already named postgres, in which case that interpretation doesn't work. I apologize if I'm mistaken, I've only setup a cluster twice and an not 100% on this.
Also, i forgot to mention the first time : kudos to everyone for the insanely good documentation, it really is outstanding!
In chapter 22.1 the following text seems to imply the role will have "the same name as the user that initialised" it and also the "role will be named postgres". Which cannot both be true, or perhaps the text is trying to say something else, but in doing so is not clear.
"This role is always a “superuser”, and by default (unless altered when running initdb) it will have the same name as the operating system user that initialized the database cluster. Customarily, this role will be named postgres. "
The words “default” and “unless altered” seem quite clear to me. In particular, the “customarily” part is accomplished usually by creating an operating system user named postgres and then running initdb as that user.
