Replacing passwords isn't the only use for voice recognition though. While the two are often done simultaneously, there are differences. The former is used in automatic transcription systems, while the latter is mostly used in security. These characteristics are found in the pitch of your voice and the colourations introduced by the vocal tract. Since each person's vocal tract is a different length and shape, every voice print is different.
Speaker identification is used to tell who's talking without their having to identify themselves.
This can be used when automatically transcribing a conversation to tell who said what. Speaker identification can also be used to keep track of people. This could be used by a large business to find people when they're not at their desk using a series of microphones. Speaker identification can also be used for more sinister purposes, often without the knowledge of those being identified. Speaker verification is using the voice to tell whether a person is who they claim they are.