It's a bit of a cheat, but with sound User experience Design (UxD) principles behind it: two small waits are better than one long one. It's why we have "please wait" messages on everything from ATMs to websites, and Hildon Desktop's own "Application loading" info messages at the top-right. The user feels the action is progressing whilst complex operations are occurring underneath.
Therefore, Apple's idea is simple: display an image of the application completely empty of content, but with the structure of its window in place as quickly as possible after launch. When the app actually opens its window, it replaces the image.
For example, the "launch image" for the iPhone's Settings app is shown on the left, with the actual app's first window on the right:
...and the Stocks app:
I've just posted to maemo-developers an idea for similar within the Hildon Desktop. For example, imagine the instant you selected File Manager from the launch menu, this image was shown:
The normal "File Manager loading" infoprint would also be shown, and then the File Manager proper would open and replace it.
Although it's "only" a few seconds we're talking about, I think it could really make ITOS feel more responsive. Given we've only got a 400MHz processor to play with, the impression of speed is just as important as the making the startup time as low as possible (but with the overhead of shared libraries etc. there's a lower bound which is achievable).
Comments, as ever, welcome.