Wikipedia has some info on your question. How accurate it is--I wouldn't know.http://en.wikipedia.org/wiki/Removal_of_Internet_Explorer
Here is one paragraph from Wikipedia:
One of Microsoft's arguments during the United States v. Microsoft trial was that removing Internet Explorer from Windows may result in system instability. At least one commentator supports this argument, and notes that removing Internet Explorer will also disable Windows Update, leaving the user without vital security updates to the operating system. This overlooks the use of a 3rd party security update solution like the browser plugin WindizUpdate that can check for and perform updates without using Windows Update. As well, almost all Windows Updates can be downloaded from the Microsoft homepage directly.