"Ubuntu's mixer applet is a different UI on the old mixer applet in gnome-applets, and not the PulseAudio-powered volume applet now in gnome-media.
In addition to the article being outdated (the treeview with the one-by-one sound event customisation is already gone), it also invents new features such as «the ability to adjust the alert volume on a per-alert basis». God knows where they got that from.
/The guy who did the last gnome-media release"
How much of the Gnome UI in Ubuntu is customized and how much of it is representative of upstream development? Be wary of attributing downstream customizations to upstream development focus.