There can be other facets to Necromancy besides interaction with spirits. Just working with spirits, contacting spirits, or speaking to the dead is done often by mediums. And most mediums do not consider themselves Necromancers.
Additional facets of the Art include: interacting with the Energy of Death for spells, Entropic meditation, visiting the Realm of the Dead, interacting with the "life energy" of others, healing/harming, interacting with the dead, creating serviators of death energy, and generally observing how Death interacts with our lives. Some are also known to worship or attempt communion with the various entities that are known to embody death.
The Art is much deeper then first glance shows, like any magic