Changed the title. I posted this because it made me think that Apple is truly becoming the most vertically integrated company in the world, from Silicon to AppStore.
In the movie, Objectified, by Gary Hustwit, the legendary designer Dieter Rams (of iconic Braun fame, the electric shaver), is asked if there is any company that really gets design today. He answers, after a moment's pause, "Apple".
My point here is Apple is integrating design down to lower levels anyone has done before. Some companies talk about corporate DNA but Apple is going to Jurassic Park levels.
While you're right that Apple didn't explicitly mandate XCode, I imagine that was considered just a bit too blantantly monopolistic for serious consideration. It seems to me a lot like the change is influenced by Apple's desire to keep developers buying Macs. They stopped short of mandating such things explicitly because they probably didn't expect to be able to get away with it, but I believe that continually high Mac adoption rates (through developers buying Macs for XCode/Apple SDKs) was the main reason for the change.
