Let me be as clear as I can be: the iOS multitasking bar does not contain “a list of all running apps”. It contains “a list of recently used apps”. The user never has to manage background tasks on iOS.

I guess I can see how this would be confusing. If it doesn’t matter – why bother letting users remove apps from the list?

Because sometimes code breaks, and it’s nice to have a backup option to shut things down. Under normal circumstances, though, you don’t have to manage which apps are “open” or “closed” to conserve battery on your iPhone.