GNOME, and Red Hat projects in general, have a long history of pushing things through with dependency nepotism. GNOME was used to push PulseAudio and Network Manager, Network Manager doesn't work without DBus, ConsoleKit and PolicyKit running, PulseAudio strongly suggests installing and enabling Avahi, Gnome Shell doesn't run outside Mutter, udev can only be built along with systemd and journald, GNOME 3 wants you to initialize the system with systemd otherwise some functionality will be broken, GNOME 3 requires GTK3 which breaks themes for any application running in GTK2, Gvfs only works through Nautilus, etc etc etc...

http://people.freebsd.org/~adamw/gnome_kde_deps/