I tend to agree with this analysis. Not only is the cost per click going down, but the amount of money they are paying out to get traffic is now at a staggering $7B a year run rate. Paying for more traffic and getting less in revenue per click shows up as a higher 'cost per revenue $' value which has gone up from 38% to 41%.

I have felt like the easy pickings have been behind them for a while but given enough money you can buy a lot of traffic. Not great traffic mind you but a lot of it.