It's possible that Google has adjusted its smart-pricing formula. But the frequent speculation that Google has "cut the publisher's share" doesn't make a lot of sense, because not all publishers are seeing a decline in EPC.
Google has just adjusted its targetting algorithm, there were to many publishers targetting the highest paying terms leading to emptying of thier budgets really quickly. On the pages where i override googles targetting algorithm, my CPM is steady. On pages where google picks what to display i'm seeing low paying high volume keywords being picked.