Britney sings live but she doesn't have to. Why? Nobody cares if it were a live performance anyways. People says when its too perfect for a live vocals, it's lipsynch, when she's scratching when she sings live, they say she's a bad live singing act. There's no winning when your Britney Spears. Atleast she's not pretending to sing all those songs when they are actually prerecorded to sound live... People have no idea here how the music industry works...
Anyway. Britney Spears will still own your faves while she's doing half-ass choreography, lipsynching and being fat on stage while your faves has to do all those exercise, belting, gimmicks etc cause if they don't, there'll be no one buying their tickets...
Horrible, but Katy's not that bad I think if you listen to her voice holistically. She also seemed nervous and like I said she really needs to perfect her falsetto...