Unlike in Apple's situation, users had the full power of choice of installing a web browser on Windows PCs. They used IE for the same reason people now installing Chrome: it's the browser where the most of the stuff doesn't break.
Microsoft was literally brought to court, and a judge said that their practices were anti competitive.
So yes, the legal system said that Microsoft was anti-competitive.
You should go read up on the court case, because it is an absolutely true fact that a judge ruled that Microsoft engaged in anti-competitive practices.
And now there are new laws, in the EU, that will prevent Apple from engaging in anti-competitive practices as well.