Well, back to topic,
I am neither with the theory that Large corporate evil Google is pocketing the difference (left wing), or the all trusting Google can do no wrong and survival to the fittest and it's your content that's worth less (right wing)
Excuse the wing analogies but had to borrow some political label since this discussion is stretching towards both ends of the spectrum leaving those in the middle homeless and unrepresented, which is pretty much how things are in politics nowadays but that's for another forum.
Simply put, Google is neither a thief, nor God!
I believe that Google is the a teenage stage, confused and confusing, testing its teeth the new way it knows how, playing with algorithms, making the ride bumpier that's all.
As for the cure to EPC downturn: Give Google less inventory and replace them with other networks or Referrals, that's what I have been doing every time earnings drop, reduce the size of Ad units from Leaderboards to banner, drop the extra link units, test and see if things pick up for you.. Worst case you will diversify even more with other networks, and usually with less inventory, Google starts to increase again the eCPM and EPC, I've never seen such an EPC drop before, but I am starting to see a slow, very slow inching in the up direction.
How about Liberal AdSensing? :)