I find it interesting that Apple continues to make changes like this.
On the one hand, it's good that Apple is adding functional enhancements and re-engineering poorly designed and thought-through components of Leopard.
On the other hand, Apple had two years between releases, and clearly Leopard was a more poorly designed and buggier than any release we have seen in a very long time. 10.4, 10.3, 10.2...none of them needed patches this large or some massive re-thinks like Leopard.
I just hope Apple learns from the Leopard experience. Some components were very poorly designed, and Leopard was--and still is--way too buggy. In general, Leopard has some very poor engineering.
Apple is going through some interesting changes. I hope it is learning and growing into a great company at "the next level."