Each initialized layout has the information about plotter, sheet format, plotstyle table.... a set of informations, in short - the (unnamed)pagesetup of this layout.
Regardless, it is possible to save all these settings as a named pagesetup.
So you can easily use such a set of settings by one click.
I will compare it with a dim style.
It is helpfull to save a lot of time (you dont need set 100 dim* variables by hand every time),
You can import this set of variables, because it's saved with a named (dimstyle/name).
Set dimstyle current, acad set 100 dim* variables for you, nothing more.
Set named pagesetup current, acad will apply these informations to the layout-pagesetup.
There is no (real) connection between named page setup and the page setup of a layout.
However, there is internally a program which checks whether the page setup of a layout matches a named page setup.
If a user changes a named page setup (command pagesetup), Autocad asks if the changes should also be applied to other page layouts of other layouts if their settings match the old named page setup.