Not only that, but I'm convinced that users are actually more efficient when perceived responsiveness is added: for instance, most users will not start thinking about what to do next on an app until they are seeing the app interface; presenting then with a non-interacting screenshot as soon as possible actually makes the overall interaction more efficient. But the ultimate is what the guys making PCalc discovered ( http://www.dragthing.com/blog/2009/07/how-to-make-your-iphon... ): you can put a non-interactive screengrab in such a way that even though it is a dumb image, touches will actually be recorded and have their effect as soon as the actual interface is set up; users can actually interact very soon. Now that's badass.
(however, most animation stuff doesn't fall in the category of perceived responsiveness, as most often, for instance for transitions, the end result must be ready before the animation begins; also, "undocumented nature"? Apple's obsession with perceived responsiveness is well-known).
(You are right about the other things you objected to in my comment.)