With respect to Microsoft, Facebook and Amazon, you are more correct. For instance, MS-DOS was originally QDOS (Quick 'n' Dirty Operating System) and bought off of another Seattle company by Microsoft.
I don't doubt that Larry Page is a talented man, but he was in the good place in the good moment. Now Google is in a dominant position and there's no place for any competition, but if Google never existed, we would have some other company doing similar things as Google. Maybe they would have appeared one year later.
Many scientific discoveries seem simple after the fact, like the Einsten's E=mc2, yet somehow it took one of the greatest minds in history of mankind to come up with it.
Indeed, at the same time as Larry Page was thinking about PageRank, Li Yanhong created and patented RankDex (a very similar page ranking algorithm) over in New Jersey - and built Baidu out of it.