I agree with what you wrote, but the comparison is apples to oranges: Google customers are businesses; end users (who CAN switch easily) are the product.

Right now the only (supposedly) viable competitor is Facebook, but it's more of an advertising duopoly that divides the market - all the people I know who advertise say that you use FB for brand/interaction/marketing and Google for sales, and for a specific spend it is usually clear which one gets it (and seldom if ever anyone other than FB or Google).