Not all recording stars' brilliance can be determined by "vocal consistancy." That's stupid.
She's brilliant (and people love her) because of her new, fresh sound - her mixing of 60's sould with current beats, her amusingly original lyrics - the whole package.
You'd be hard pressed to find a pop singer that has a perfectly "consistant" voice.
"If you are going to do something, do it well. And leave something witchy."
-Charlie Manson