Earlier quoted context omitted.
What you're missing here is that Apple bans everyone equally while Microsoft does not. What I mean by that is the App Store doesn't discriminate on an individual basis. Apple is generally consistent in their "unfairness". Looking at what Microsoft is doing, their decision to restrict Firefox immediately struck me as an anti-trust monopoly issue. They're not restricting Firefox on the basis of some policy that applies…
You don't think Apple decided to restrict third party browsers so their browser "can have a leg up?" (Yes, yes, I know the answer will come back "a unified browser is a better user experience". And my response is: why not let the market make that call?) That sounds awfully naive. Apple certainly does protect its turf (c.f. banning Google Voice after approving dozens of VoIP apps) , and to argue otherwise is just sill…
Looking at the continuing success of iOS, so far, the market isn't really shouting out loud that not allowing third party browsers is a good thing.
Also, I think there is a valid technical argument for not allowing multiple competing libraries on a mobile device: memory usage. All else being equal, if I have multiple apps, each using a HTML renderer, I would prefer them to share code, browser cache, etc, just as I would prefer all my applications to share their font rendering code, 3D graphics library, etc.
Someone arguing for inclusion of Firefox on iOS or Windows Should, IMO, put convincing arguments on the table why that "all else being equal" phrase does not hold.