I would say that neither company is a monopoly, although Microsoft skates a bit closer to the term than Google. I base this on the strict dictionary definition of the term. In the very competitive environment of Internet companies we now have, neither Google nor Microsoft has exclusive control over any resource that people access. Nor does either one have sufficient influence that they can effectively control prices paid for most internet-based resources. Microsoft has some degree of control over they charge for their end-user software. Google, because many of their products and services are provided free due to advertising revenue -- really has no price to control.
Is Google the only search engine around? No. Is Microsoft the only business application or operating system company around? Apple and Linux vendors would surely say no. Do both companies compete very actively in their markets? Of course. Those that don't play the game to win will be consigned to the ranks of losers. I don't see that changing anytime soon. Neither of these companies wants to be there, that's for sure.
If anyone bandies around the 'monopoly' term when it comes to today's Internet market, they're probably doing it more for marketing or FUD reasons than for any real legal purpose. At least that's the way I see it.
I would argue that Google is not a monopoly even though it shares many of the characteristics that Microsoft did during the time of Bill Gates.
For starters, there are other search options available to everyone and many people routinely use these options. I cannot begin to tell you the number of people that I routinely come across who say they are going to 'Google' something and yet use the default search engine associated with their home page (often Yahoo or Bing).
In addition, Microsoft often restricted the use of other operating systems on computers that ran Windows (or at least discouraged it by making it difficult enough that only a savvy user could dual-boot). Google does not restrict the use of search engine choice. Even on my son's Android phone, he is not restricted to using Google searches.
Finally, if I recall correctly, one of the criteria for determining if a firm has a monopoly is the ability and/or tendency to use their market position to control the market. I don't see Google doing such, mostly because of the aforementioned reasons but also because search engines are a free resource to the user community. Yes, there is money to be had (or Google would not be in business), but it would be nearly impossible to control the market from a fiscal perspective. Granted, Google can (and I believe often do) control the advertising dollars through exclusivity but, as I see it, that is a horse of a different color.
I have a REAL problem with anyone referring to Google as a monopoly. Last time I checked, there were literally dozens of search engines out there -- Bing, Yahoo, Lycos, AltaVista, Excite, etc.
This once great nation has become entrapped by the idiot Obama-Pelosi-Reid liberal mentality of 'how DARE you become successful.' Google has endless competitors out there, but because it is the best at what it does, it is demonized by the communist left of this country and labeled as a 'monopoly.' The left should really try looking up the word sometime...