There are good reasons to use a splash page rather than a "fake UI" image. For single-purpose apps (say, Calculator, or Weather) the state of the UI post-launch is easily predictable, so you can actually make a splash image that lines up with what the user sees after.
For more complex apps, especially apps that maintain state, this becomes impossible. You can make your splash image your "home" view controller, but if the app is launched from a URL (a large use case for many apps) the user will see an "empty UI" that is not what they're looking for, suddenly replaced by UI they are looking for.
Making matters a bit worse is that, at least up until iOS6, switching between apps (not just a cold launch) can also show the splash image briefly - but your app snapshot remains in memory, so you cannot guarantee the "empty UI" is what your user actually ends up looking at.
Splash images suck, but for a lot of apps they are the least of several evils.
