If there's anywhere to point "blame" it would probably be the #GNOME team. So far as I can tell GNOME centers the time over the desktop window snap-to area.
This *does* make a certain kind of sense. I just can't understand why they would've chosen that behavior when the default GNOME experience is to have a single bar that runs the full width of the monitor. Why *not* center it to the container it's within? I have to assume there was a reason ...