Google's Smart Pricing has been a well-kept secret till now. Basically, if you are a Google Adsense publisher running a network of sites, one low-performing website could cause Google to lower the ad prices (EPC) of all sites in your account.
Smart Pricing "black-box" techniques are definitely a cause of worry for Adsense publishers. I have personally seen my earning drop when I started showing Google Ads on another less-popular website. Once I removed ads from this website, it took about 7-10 days until my earnings graph hit the normal mark.
I wish Google had been more open about Smart Pricing. AdSense Publisher Support did try to clear the misconceptions but that may not be enough to satisfy Publishers.