KDEnLive is a KDE application and most people here use GNOME. However, all
of the *buntus share the same repositories so some will be running it
anyway. Not everybody sticks with the default applications (Ubuntu ships
with PiTiVi).

The sound is configured in the settings because many people who edit videos
have multiple sound and video cards. Your setup may be simple but some
people use Myth TV and have a graphics card for the computer, a TV card or
two and more graphics cards. Some of those will have built in sound cards
and others will need more than one sound card to work with the various
graphics cards.