Shifting money back and forth between different departments may be fun for you, but unnecessary in the real world unless you have different corporations set up. And last I checked AdWords isn't a company in itself. If you don't see how that's pointless then I'm sorry for you.
Shifting money back and forth between different departments isn't fun, not even for me! unless it is in the best interest of the business. If I understand your point, what you are saying is "why would the adsense team care about the CPC since the money goes to google anyway?" First, all the money doesn't go to google because publishers get a share of the CPC thus decreasing it is logical. Second, I think that the adsense team acts like a customer for the adwords one in order to preserve competition and to boost performance. it is an internal organisation where departements act like separate "business units" but I cannot confirm that.