Although Google is constantly tinkering with the ranking algorithm that puts you in the number one spot (of course) and your competitor on page two hundred and fifteen, occasionally they make big shifts and tell the world about it.
We can welome the latest seismic shift, as it promises to deal justice to search engine optimisation cowboys, the kind of companies who create pages of junk content in order to create well ranked pages which are then sold on to genuine companies who just want to have a presence on the web. The junk content can be copies of other content, or just random phrases stuffed with certain keywords. The other way it can be used by cowboys is to link to websites who are paying these people to generate links.
Google will never genuinely know which websites represent the most authentic and reliable companies, but each of these shifts is an attempt to do slightly better at it.