Google is not a monopoly. It has numerous competitors and only really remains in the lead because it is perceived to be the highest in quality.

Power law distribution in search engine market share. It also explains why Coca Cola is the dominant cola to name another example.

I particularly like Peter Thiel's explanation of the power law, used in relation to VCs fund performance: http://blakemasters.com/post/21869934240/peter-thiels-cs183-...