I wonder why such a big website network like About.com uses adsense. If it were me, I'd start my own advertising network. Do you think they are related in some way?
Why spend money to develop a publishing network when one is already in place that does the job just fine? And if that one doesn't work try one of the thousands of other ones out there. After all how many times does the wheel need to be reinvented before people figure out it's still just a wheel and the vehicle is what matters.