The amount of people CC'd in on a work email is proportionate to the amount the sender is covering his or her ass, plus the amount that they want to escalate a matter to upper managment without looking like they are actually doing so.

So as an issue turns into a flaming crapstorm, you'll see more and more people CC'd in on a mail, and the level of upper management increase.

It will, in fact, be the case that 99% of these people will have nothing to do with solving a problem and a good 50% will delete all the emails without reading them.