Well here is the deal.
1. It's almost an impossible song to sing, the range required is beyond most vocalists.
2. (This is critical here) Without a band to give you a key, the natural tendency is to start a couple of notes too high, and when you do that, you run out of range at the top of the song (what so proudly we hailed) and you really butcher it, because the only choice you have at that moment is to go low (flat) and just suck.
3. Jerry Jones wanted Faith Hill to do it. She refused, and FOX said NO NO NO NO, because she does the theme to some other networks football show. But the real deal is, she said no, lot of people do, it's a gig from hell. I'll bet that CA was not the second choice either, or even the third.
I mean there VG, how come they had to go find some LA girl, and couldn't not find one of the several outstanding Texas talents (or even one of the thousands of mediocre Texas talents) to do it. Because they all said 'no.' No one in their right mind wants to do that song (Beyoncé excluded, who BTW, rocked it - and that's why she's Beyonce, and the other two girls in Destiny's Child, are who? Yeah, two other girls, not Beyonce.) on world-wide TV, live, in a stadium, without any accompaniment.
But go for it Rex, let me see how you pull off walking out in front of all of those people, 100,000+, and the cameras, and not let it bother you. It's remarkably harder than it looks. It turns out it's not like doing it in your bedroom singing into your hairbrush. It's like some kid who sits on the bed and shreds the guitar thinking he's Kirk Hammett. He's not, he's only playing one song, over and over again until he gets it right, while Kirk is doing 2.5 hours of that a night, on cue, at 9, every night of the tour.
I mean it might look easy, but the reason they are multi-millionaires (other than luck) is that it's a lot harder than it looks.
