Actually, they don't have to be running at all times on Android either. Apps can request to have a portion of them run on a periodic, or in 2.0 and above they

Actually, they don't have to be running at all times on Android either. Apps can request to have a portion of them run on a periodic, or in 2.0 and above they can register a sync adapter with the OS sync manager. The sync manager handles scheduling and running of any registered sync adapters, and can adjust their schedules to minimize used radio time, and hence used battery life.