The two things that have ruined modern music are compressed mastering and vocal pitch correction. Combined, they have rendered most new music unlistenable. Some of the shit that Melodyne is working on now is scary.
As for Britney, in the studio she doesn't have to sing more than a line or two at a time, that shit is edited together from dozens of takes. So she still doesn't have to be all that great a singer for them to create an acceptable take.
You think Rock artists from the 60-90's didn't edit their vocals or combine multiple takes into one track?
Every single studio album has been mixed and technologically enhanced to the best that that era's technology allowed.
VH for example. You think Sammy Hagar just sang the track once? I guarantee he sang some of those tracks 100's of times to get them perfect for studio production. Sammy is a great singer.
Anyways,
I hate brittany spears music, but she doesn't suck.