Is a mobile OS any different from a desktop OS?
When it comes to how programs open and stop, yes. On a desktop system, its the user who starts and stops the applications. However in the mobile world, the user only starts the application, its the OS that stops it. This can cause what the development community calls garbage and the more garbage your OS collects, the slower it can get. Windows Phone 7 handles this garbage, or background applications much differently then other operating systems.