Well,
I think with some of the performers, it was not so much about appropriate key, as it was that their voices were just not in shape. I mean, there was NO appropriate key for the Flock of Seagulls guy.
With Tiffany, it was not neccesarily the high notes that she didn't get....for instance when she goes something like "tumble to the groung and then we SAY"...instead of hitting the root note, she hit a third up....would have been ok, but she hit a little flat. It was more about her trying to embellish the songs and it not quite coming off right.
I think that CeCe did pretty good, but I have to disagree with the assesment that Arrested Development did not deserve to win.
While CeCe did a respectable job with a simple cover, Arrested Development reinvented the Los Lonely Boys tune. More importantly, they were probably better than they originally were! CeCe was good, but let it go a little. She also hit a couple notes that weren't exactly right, but didn't sound horrible either... like instead of singing a run, root , third, fith.... she sang, root, fourth, fifth. Not a humongous deal, but not exactly right.
I was very impressed with Arrested Development, and enjoyed them more than I did during their original run. They entertained, and everything was INTENTIONAL. If you aren't into rap, you might not have been moved. I personally, would love to see what they can still do. It was a breath of fresh air to hear someone approaching rap in that way.