Why would Google want to continually change the face of SEO? Surely it is in Googles interest to be transparent and to let people know what to do to get to the top.
Google have an interest in providing high quality search results (i.e. good relevant search results). However, Google don’t do this because they are nice people (though I am sure that they are). Google is a company, a business, an enterprise and their primary interest like any other business is to make money for shareholders.
Google’s main revenue stream is paid for advertising and they make an enormous amout of money out of this advertising! Therefore, Google continually strives to increase the revenue from advertising and Google search is the primary vehicle with which to achieve this.
As long as there is a secret element to the Google algorithm and as long as this Google algorithm changes, Google have the control they need to be able to sell more adverts. This will always be the case.
This approach also keeps good SEO experts in business because the only way to keep up with changes is to do this as a full time, dedicated occupation and there is a huge amount of work just keeping up and rolling out the changes. Site owners therefore have little option other than to pay for adverts or employ a competent SEO person if they want to be found on the web.
The roll out of the Panda update was a clear example of Google flexing its muscles and changing the SEO space. Also, the strong suggestion that agility to change is key and that site owners need to keep up with the continual changes Google is making proves that change is here to stay and there will never be a ‘perfect algorithm’ (even if it was possible).