I hope this is good enough for the Prospectus. Let me know if I'm doing something wrong or treading in someone else's territory.
In Microsoft's monopoly court hearings in 1999, it was deemed that the company was using its huge market share to push out and eliminate the competition. At the time of the CNN Money article, Microsoft was on ninety-percent of desktops. Google has control of fifty percent of its market, but it has similar practices of using its large user bases to move into other markets. For example, one company beat Google to the punch about a collaborative spreadsheet application, so Google buys their competitor and puts out a similar product. The smaller company can not compete with Google's user base. For now, Google has a few competitors like Yahoo and Microsoft but its market share is growing rapidly.
P.S.- I want to address the question of the fine line between monopoly and just being the best at what you do. Again, let me know if I need to add anything.