Windows was/is two OSes - one stemming from Win3x, the other from WinNT.With you so far.
IE was an afterthought.Still with you.
To get it to work the same way on both systems required merging the concept of browsing into the OS - in the same way that the Windows device context required merging the WM inextricably into the OS.But Mozilla works on both platforms (and more) and works in exactly the same way.
Yet Mozilla isn't welded into the OS.
And Mozilla offers the same functionality as IE.
The same with Opera.
I think you're wrong on this.