The blog post is better explained, but in summary it is stated that Google has made a play that is probably the cause that AdSense earnings have almost halved.
Here is the fourth reason:
4. Google removed half of the offer and sent it to its own coffers.
… Google has secured that has begun to "do tests, whether these work or not", in places like Google News, Google Image Search and Youtube. With this, the only beneficiary is Google because it is the owner of those spaces.
It means then that Google has possibly taken half of the AdWords offer and sent it to these own sites leaving us scratching the kettle. His argument has been that he has done it to benefit advertisers although that benefits him more himself.
"Of course, these experiments benefit Google because they generate revenue from new sources - but by ensuring that we show the right ads at the right time to the right people, we'll add value for users too"
It's like you have 1,000 advertisers, who pay you $ 100 a month to place their ads on 1,000 taxis. Each taxi driver takes 100 dollars at the end of each month. So Google decides to remove 500 ads and place them on 500 of its own taxis, which would make each taxi driver now only have 50 and the experiment leaves him a modest amount of $ 50,000 in addition to what he already earned.
Go there and read it completely.