I was wondering too about the wisdom of this move, but it shows that they are not going to hitch their wagon to anyone's horse but their own, and that they have the ability to modify the horse to pull whatever load is necessary at that moment, a new iPad, new iPhone, AppleTV,
If you're going to discuss consumer electronics manufacturers getting screwed by IDMs and commodity chips, the best example is the first Xbox. Microsoft went with Intel, but Intel's business is offering faster chips for the same price, not the same chip at lower prices every couple years. Some MS ended up with a chip that never got cheap enough. With the second Xbox, Microsoft also designed its own chip (licensed tech from IBM rather than ARM) and they've been shrinking that sucker constantly. Console margins have been increasing constantly.
Apple may hope to have "new" products using the A4 years from now using an A4 that's 1/8th the current cost. That's what owning your own chip allows... not necessarily some awesome roadmap where there's an A8 four years from now, but a roadmap where the phone's using the same processor with very minor redesigns for a fraction of the cost now. It's not that owning the IP allows them to upgrade faster, it's that it allows them to increase margins faster by stringing along the manufacture of the same old chip beyond the point where an IDM would retire it and push something faster and more expensive. Oh, they may call the next thing an A6 or whatever, but the processor performance will eventually be deemed "good enough" and they'll widen their margins on that part and they'll start pushing the other features like much improved battery life.