The crowd at Fenway Park picks up the tune when a disabled man dissolves into nervous giggles (also, note that this man gets further into the song without making mistakes than Xtina does!). Everyone sounds great.
The crowd at a minor league hockey game in Virginia finishes the anthem when a little girl's mic cuts out. They sound even better than the Fenway crowd!
What I'm saying is, yes, The Star-Spangled Banner is kind of a difficult song for any one person to sing, but it actually sounds good when sung by a crowd. Which makes sense, given that the tune comes from a drinking song. Who sings drinking songs as dramatic solos?** And even if people mess up the words, there are enough other people singing to cover for it.
I'm not saying a solo version of The Star-Spangled Banner can't succeed - I've got a soft spot and a half for Rene Rancourt***, for example:
To me, the most successful performances of The Star-Spangled Banner are the ones that let the crowd sing along! But no, no one just sings the damn song straight, everyone wants to show off! I wish we could have the singer(s) get the song started and then let the crowd take over. I think the main barrier is not the difficulty, but just that it's a long song - I don't know if everyone would stay in for the whole thing (without an adorable child or intellectually-challenged person to support).
And it's not going to happen, because people want their chances to show off, and even with eleventy-million professional, semi-pro, college, high school, and peewee sports games being played in the US every year, there eleventy-one million stars, starlets, kids, acapella groups, military bands, and state troopers itching to perform their souped-up versions of the national anthem. And maybe because we've all been taught that The Star-Spangled Banner is too difficult for ordinary people to sing.
But it's not! Really! Together we can perform this song! Let's do it! We'll sound great!
*Connecticut's #1 for Hip-Hop and R&B - I'm mostly an NPR girl, but I can't stand Cokie Roberts' "analysis", so every Monday morning when she comes on, it's Hot 93.7 all the way.
**Ooh, now I'm tempted to record an extended, melisma-filled version of, I don't know, "The Irish Rover" or something.
***Although really I think I like Rene Rancourt's O Canada even better than his Star-Spangled Banner. Observe this fabulous example of classy passive-aggressiveness exhibited by Rancourt and a Garden full of Bruins fans after Canadiens fans booed the Star-Spangled Banner in Montreal: