It's funny that people do things like that though. It really has the opposite effect on your voice that you intend it to have. I don't pay much attention to it; I think a great part of it is just the drama of the performance: shaking your hand in the air, pounding your chest, bending over, stomping your feet... it's all getting into the song.

If she actually did stop doing this around 2000, I would have to guess that it was because she finally learned that it isn't any help to your voice. Interestingly enough, it was probably around that time that her voice really started to open up and flow out a lot more easily.