Oh gawd
Britney sang "You Oughta Know" live and she's been known to sing along live with a loud backing track. She's one of those who can't control her voice live when in motion.
There are artists that are just born with it... Xtina, Beyonce, and Britney. They have the potential to sell of course.
While there are also those that are not naturals but because of training and the right connections they were able to accomplish something, ie. Miley Cyrus