lip sync was done on both sides of the pond well before pop ever raised the ugly spector... err, specter of Janet Jackson's supernipple, or even the Beatles. Many shows had artists (ie talent) mouthing to their records, or even to pre-recorded versions of their material recorded specifically for the lipsync. The Beeb did it a lot, and now finds artists who can't actually perform live specifically demanding it.
Many great bands went to the Beeb studios to pre-record live versions of tracks they were later to "mime" to. If the artist in question wanted (or was/were forced into) the exposure of TV, he/she/they had to pre-record and then mime. That way, they were miming to what they'd done especially for the show, as it were. Silly, yet nothing new, nothing special, not even a sign'o'the'times. It happens all around us, from the government on down.
At least some of these "lost takes" can be recovered and salvaged for killer box sets.
A great book should be written about this "protective" process... the supposed "5 second delay" on radio, etc. If it has, I've not read it. It has a great deal to do with radio security, which takes us right back to Churchill.
Sorry, I can't explain further right now. I'm getting my computer back together so I can update the Faces site again soon. I had a crash the other day that took even me by suprise.
C'est la vie!