Parameter port on p:parameters

Can anyone remind me why the parameters input port on p:parameters
is explicitly *not* a primary parameter input port?

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | The firmest line that can be drawn upon
http://nwalsh.com/            | the smoothest paper is still jagged
                              | edges if seen through a microscope.
                              | This does not matter until important
                              | deductions are made on the supposition
                              | that there are no jagged edges.--Samuel
                              | Butler (II)