Why no one mentions the real power behind multi-tasking in Android (which iOS doesnt have)? i.e. tasks/apps scheduling based on intents.
In Android, apps are automatically started in the background when certain events/intents occurred. e.g. Android will periodically starts the rss reader in background to refresh posts when a timer event occurs. Or apps that only come alive when a call/sms/email/location event comes in. Or apps that refreshes widgets etc.
It is irrelevant whether an Android app is running in the background. What is relevant is the app is activated in the background as and when it is needed. This is much more efficient than having "background" apps which take up RAM and most of the time isnt doing anything. For those apps that require constant connection (llike IMs, voip) Android has the support for "service" app which keeps the apps alive in the background.
For current iOS if you need the app to periodically do stuff then you need to have it as a background app. You can only keep a limited number of apps active in the background before you run out of RAM. And there is a strict limitation of what kind of apps can run in the background. Those apps that do not satisfy Apple requirements cannot be run in the background.
For Android, you can run (theoretically) as many apps in the "background" since Android only load/unload the app in/out of RAM when it is need/not needed. And Android does not impose any limitation on whose apps can stay alive all the time (i.e service apps) or those that periodically run.