Because neither Apple or Google have a monopoly on the browser market anywhere near what Microsoft had. Also, Microsoft was sued for actively thwarting competition[1] in order to maintain it's position.
While your first point is valid, the fact that Apple completely refuse to allow any 3rd party browsers on iPhone/iPad/etc... puts them in a worse position competition-thwarting-wise than MS with IE.
1. http://en.wikipedia.org/wiki/United_States_v._Microsoft