No, PR was not revolutionary at all, neither was it "invented" by Google.
Eugene Garfield, William Goffman, Jon Kleinberg, Sougata Mukerjea, Peter Pirolli, James Pitkow and especially Ron Weiss, Bienvenido Velez, Mark Sheldon, Chanatip Manprempre, Peter Scilagyi, David Gifford and Andrzej Duda (which finalized the concept of "hierarchical network search engine that exploits content-link hypertext clustering"), are the real inventors of something new in nature.
They are all rightly recognized as the decisive influence in Google's PR work.
Hilltop was brought to light as a variation of other connectivity based algorithms (so nothing esentially new), by Krishna Bharat (working for Compaq at the time) and George Mihaila (from University of Toronto).
Many other new Google "gadgets" came as a result of pure money spending needs.
After going public, they raised the money for... what?
They couldn't use all the money for significantly improving web search so they needed expansion into another related areas.
It seems it's going well for them in those areas too and I hope they will survive as "the boys" are good guys after all. Yes, I am very supportive for the "do no evil" and "f*ck greed" philosophy.
Please do not exaggerate.
Almost the same as saying that Microsoft has invented anything.
Google was the logical answer to higher demands of net community. It is/was a natural process.
If not Google then someone else would take the position.
Again, it was not some bright new invention which revolutionized some aspect of our lives.
They perfected already widely used technique(s), nothing else.