Some Microsoft updates did disable Netscape and not in the nice "do you want this to be your default browser" kind of way. Not that MS was the only one; a version of Netscape disabled IE's ability to display XML of all things. http://news.cnet.com/Microsoft-advises-IE-users-to-uninstall... (However, based on the late date I think this was more done out of spite than anything else.)
There are older examples that predate the popularity of the Internet: Microsoft specifically made earlier versions of Windows rely on DOS only work with Microsoft provided DOS and not DR-DOS.
