Judging from a technical point-of-view, Google uses usage data in order to improve search results. It is widely mentioned in publications as a method to improve search rankings, and therefor I think it's an educated guess that Google is using these known parameters to improve their rankings. It is actually considered one of their main competitive advantages that makes it impossible to reach their level of relevancy without holding the same behavior data they hold. One of the pillars of search engines is a reference model which you can check and see if you improved your results. User behavior data creates a great reference model, and helps you evaluate your algorithm changes and improve.
It is far more complex than
if (someone clicked me on page 5) -> next time page 4
There are many inbound factors, and CTR rates are just one parameter. You can read a bit more about it here and by studying relevant patents Google submitted.