Are there any apps in particular for which you feel that this behavior is worse? It's supposed to be for document-centric applications or those that do something useful in the background (eg. iTunes). On Windows, the latter category tends to clutter up the system tray, while the former category just forces the user to wait for the whole application to re-launch if the last document was closed. Splash screens are mostly a thing of the past, but app launch times are still noticeable, and re-activating an application that was merely swapped out by the OS is faster than a cold start of the app.