For each his own. But i find it selfish to make an artist feel like they have to "fit" a certain style. There are so many singers out there that give different types of vocal delivery. Love Bran for her style and her approach to music. And if she is no longer giving you what you need in YOUR current mood in life, then move on to another artist who will. But to say "I'm over this from her, I now want this from her..." is almost selfish.
And no, it's not putting the artist in a box and saying you can't experiment a bit. But it should be at the will of the artist not at the will of a fickle fan base.
Also, when I say "you" i'm referring to the general pop, not anyone individually.