I love karaoke. DO you?
Yes, karaoke is often implemented by recording engineers in reference to version of recording with instruments too.
Do they have to record things separate from what they use in the originals? 
There are many artists that will often record and can't afford a band/orchestra so they will use karoake recording.
That is very interesting. I have not heard that, but it makes sense.
Some people think it's the same thing as lip synching but it isn't. That's where the singer will mimic a song that has already been made and already has a lead vocal.
Is karaoke popular outside of the US too?
It is, beginning back in the 60s, being able to store audio and make it portable became very popular in the music recording industry. It became a norm for musicians all around the world.