Whether you personally like the anthem straight forward or "stylized" is a complete red herring here. It's inconsequential.
Artists get to decide how to interpret a piece and perform it. Christina Aguilera sings with lots of runs and ornamentation--that is her style. Why on earth would anyone hire her and expect her to suddenly start singing like Charlotte Church? The runs and extras don't factor into the equation here, because that's most likely what she was *expected* to do, based on all her previous performances and history. She's wasn't disrespecting anything--she didn't mock its value, she just sang it in her style--that's what singers are hired to do. For example, my mom whines and complains that she wants people to help her with things, then she stands there and tells them how to do it--she wants them done *her* way--if you want something done your way, you do it yourself--don't expect someone else to change their entire way of doing something because its your preference. If you want the job done X way, you hire someone who does it X way. You don't hire someone who does it Y and make a big stink about it.
As for her flub--it was an honest mistake. There are tons of professional musicians who make mistakes *every* day. You'd be hard pressed to name one legendary musician who hasn't. They flub lines, miss cues, miss notes, miss riffs--because there's a lot going on when you perform. There's adrenaline and nerves and sometimes things just get messed up. Aguilera has done riffs plenty of times in high stress situations--it just wasn't her night--it happens. It's like claiming a champion figure skater isn't a professional or up to standards because they miss a jump, or slip on a simple part of their routine--they've done it a thousand times, right? Shouldn't they have practiced it?
One honest mistake (even at a venue as large as the superbowl) does not equal gross incompetence or lack of professionalism. In fact, as any musician will tell you--a true test of professionalism is how you handle mistakes, because inevitably in your career you will make one or be at the mercy of them from your colleagues, sound or lighting people.