I think that if she used her high voice, people would be all "Wtf. You're 28. >>"
Anyways, I think the Raise your hands! and YEAH YEAAHHs are vital, as remember, this was a LIVE show, and you're kinda just sitting/standing in the audience..
She does it because she's an awesome entertainer <33 I mean if you went to some huge popstar's concert, would you want them to avoid hyping you up? :|