Now that the AppScaffold uses the ViewController model, I guess that it would be possible to load the game view from within a normal UIKit type app, eg. have a table list controller which to select which game needs to be played.
In these circumstances it would be definately be better if the game view controller released the memory, as the UIKit parent of the game may unload the game.
I know this isn't normal UI for a "game" but the sorts of things I'm doing with Sparrow are not all "games" - Sparrow has much wider use eg. I'm about to start building an app where I'm using Sparrow as part of a diagram drawing tool