The point of forcing MS to open up Windows to competition is because MS can make it hard for competitors to offer the alternatives. By locking out products they fortify their monopoly.
But with Google, there is absolutely nothing forcing you to use their website. You can just as easily go to Live.com. And in Firefox you can add your own custom search provider. It is very easy to do and you could even add one for Live.com and make it your
default. I set up one to search MSDN.
The problem with the monopoly is that it kills competition.