When an outsider enters the picture, the picture changes. Something like the Hawthorne effect in anthropology. The very act of recording someone singing can change how the singer approaches a song and thus presents it. We know that because it happens. People who have recorded songs know that it's a good take so far. Enter that thought and suddenly the singer's BP is up a bit, breathing goes funny and the take ends up being junk only fit for the editing-room floor. Remember the first time you heard your voice after it had been recorded. A majority of people say, "That's not me," or "My voice doesn't sound like that." Intermediaries inevitably affect the material they are recording. It seems to be ubiquitous in all forms of human interaction, and I don't really understand why we'd expect this area of human endeavor to be substantially different. YMMV, and that's cool with me.