FoxyPage:
What's the point of the "aerobics" on her part though? Do you think Robert Plant or Mick Jagger would let their gymnastics interfere with their singing?
You're comparing pop performances to rock performances?
Pop is much different. A lot of the performance has to do with dancing. Rockers don't really dance much, they just mostly sing. Pop stars do all the dancing. That's what a lot of the focus is on. Plus, a lot of pop fans are young. You can't expect a kid to be interested in watching someone pace while they sing. They want a big show, something that will keep their attention, something fun to look at.
Two different styles of music, two different styles of performances. It's easy to just walk back and forth on stage and sing for two hours than it is to actually dance for two hours, or at least most of those two hours, since they will likely be able to sit for a song or two, if it's a ballad.
It's just the style of music. Practically every pop star dances like crazy when they perform. The point is to put on a good show and keep people entertained.