The fact still remains that Apple made a big promise without analyzing all the legal aspects of it. Most average to big size companies do the reverse of it - Make sure the legalities are in their favor before making big announcements.
Are mistakes not possible in your world? Somehow I doubt even an exhaustive legal analysis would have turned up a patent troll. (Kind of characteristic of patent trolls, really)
It's hard to know what really happened, but the story is that it was basically Steve Jobs who made that big promise himself. It is said (and again, who knows if this is true, but that's the story) that the first time the FaceTime engineers heard about making it an open standard was when Steve announced it to the world.
Open sourcing Swift, on the other hand, is clearly something they've been planning for a while with the full knowledge of all involved and wasn't just a sudden impulsive sort of thing.
