If history is any indication, by the next OS update (4.2 or 5) they will be merged. Apple seems to prefer to keep its horses decoupled: technologies percolate more slowly through its stack, but it allows them not to get stuck (so much).
For example with Longhorn MS tried to change the underlying kernel, the user interface, and to add some of those changes in its main programs too. Apple instead can take up to 2-3 iterations for a technology to become entrenched: first its developed in some niche application (e.g. Core Animation in iOS), then it gets generalised and turned into a general framework, and finally later its application groups (iLife, iWorks, etc...) start making use of it.
(note: I am not saying either system is the best. They both have pros and cons)