What Facebook is trying to do is completely different... you were always able to use non-microsoft products/programs on Windows or browse non-microsoft websites... what Facebook is trying to do is much worst (probably evil).
You could also view it as not too different. Windows wanted to be the platform under everything. Now Facebook wants to be the platform under everything, and content/apps will have to go through Facebook (look at the direct publishing stuff they're already doing).
You don't have to go through Microsoft to publish Windows apps... not sure if it changed with Windows 10 though... but of course they are trying to change that to be like Android and iOS and get complete control.
But the big difference is: you could reverse engineer Microsoft Windows to do what you want beyond the APIs provided but you can't reverse engineer Facebook because you don't have the code running on your machine.
