Microsoft did not get in trouble for not allowing other browsers. They have always allowed any software to be installed. They got in trouble for making it the default and including it in the installation without giving the user a choice. You have always been able to add any browser you want to Windows. Same for the media player. Apple did all the things Microsoft got sued for as well, but got away with it because they are the "little guy". It wasn't seen as abusing a monopoly.