BTW, speaking of anyone being a pop star...
Get a load of this video :
HOW TO CREATE A SEXY POP STAR. That tells you how technology like a software called AUTOTUNE can make a looker who can’t sing a pop singing sensation :
http://youtube.com/watch?v=irk3_p15RJY
You have autotune (which can happen real time and can be used on stage) and vocaline which will replace one track with another, keeping the first timing if so desired. Used mostly for vocal replacements in movies (but also works with music). This used to be quite challenging for certain actors. If you are anywhere within 1 second of the timing, it will compensate for you and match things up.
Add to that all the editing capabilities, notes and rhythm repairs and replacements and generally anything photoshop can do visually, there are the same capabilities in audio. Just like you shouldn’t believe your eyes any longer, you shouldn’t believe your ears.