Wav's, Mp3's, CD's, etc are all technically 'streamed' audio, meaning all the individual instruments and vocals that make up the file are simply recorded as a single track. When you buy a CD, its streamed music. However, when the musician actually makes the music and has it recorded in a studio, each instrument is set up on its own channel and recorded individually. This way if one instrument turns out too loud, or too soft in the final track, its easy to adjust the volume, or make any changes necessary with only affecting one instrument (or a voice). If the music was initially recorded as a stream, it would be impossible to fine tune individual aspects... just the same way it is kinda impossible to remove the voice in a song from a stream, because its already mixed together.
An example of a multichannel music file would be a MIDI. However a MIDI can't contain vocals. A module (MOD, S3M, XM, IT) can contain vocals, which can be removed if you wanted. None of these are streamed files, though