Britneys voice is very versatile.
She can reach very high and low notes.
Obviosuly shes not more talanted than Whitney was, but she does have an amazing voice, believe it or not. Her voice is more versatile than Gagas.
If you've been following American Idol this season you would know that performances have virtually no impact anymore. This being the final it will probably do a little more, but keep that in mind.
Not that it matters. Where Have You Been has a bullet of 1800 on pop and is approaching the top 10 on iTunes. Anyone that's still gonna deny it's gonna be a hit is delusional.