In many of the later generation aircraft that you allude to, a great number of separate control panel functions, such as IRS position entry panels, have been incorporated into the FMC/FMS CDUs. Also in pre GPS/IRS times, the facility was required to update Inertial position if drifting excessively. This facility to allow Lat and Long insertion entry to the IRS still exists in the FMC/FMS, but is basically redundant due to GPS position updating.
On the B777 aircraft, even the PA is selectable on FMC CDU #3.
That's the quick and dirty answer, I'm sure that others will come up with better sharp pencil answers.
Best Regards,
Old Smokey