This will happen more often on older recordings where there is a very clear separation of different parts of the recording (instruments, voice etc...) between left and right. More modern recordings will have a fuller sound spread between both sides. I am sure there is a technical term/explanation for this but I am neither a musician or producer so just giving a laymans view.
Stereo recordings are done with two microphones (or one microphone that acts like two)... In older recordings (or oddly mastered modern recordings), one microphone recorded the music, one recorded the vocal part... I've found that if I listen to (I believe it's) Penny Lane, one side has the vocal and horns, the rest has the guitars/drums.