Google is effectively a monopoly, however the issue here is that they do not appear to be misusing their monopoly. Microsoft has been convicted of using illegal tactics to build and maintain their monopoly like licensing agreements that effectively shut competitors out of the OEM operating system business. Apple has been accused of abusing their monopoly by leveraging their position in music players into dominance in online music sales and then enchaining the two the way Microsoft enchained Office and Windows dominance.

What, exactly, have Google done to shut competitors out of the search business? What agreements have they forced on advertisers to discourage them from advertising with anyone else?

And while they ship other products that leverage their competence in search, they do not appear to enchain them. For example, they dominate in online search and have a strong position in online mail. And yes, they can leverage scale to sell advertising on both properties. However, their does not appear to be a link between the two products. For example, when I perform a web search it does not appear to use my mail inbox to influence the relevance rankings of online search.

So far, Google appears to be following a different strategic path than Microsoft did.