Often times with televised performances (as is the case often with National Anthem singing especially), the TV audience hears the pre-recorded track, but the stadium audience hears the singer sing live. I BELIEVE this is what the case was with Whitney Houston's so infamous National Anthem singing at The Superbowl (that or it was just flat out lip synced). There are quite a few artists who sing full songs live these days, removing my biases, most of the relevant female artists in the industry do, but when you go to see an artist like P!nk live (who claims to have never used and will never use a backing track), you're hearing her back up singers a LOT. Especially with her, it's to the point you don't even hear her voice sometimes. The problem is that nowadays, there's so many different layers added into the studio versions of songs that it's impossible to get even a similar sound by just having the main artist sing that song with a band or instrumental.