The app switcher is not a list of open apps, it is a list of recently used apps. Any of those apps may already be closed by the system, and many of the "older" ones probably are. In that case you are simply removing the screen image from the list and nothing more.
The system closes apps silently when it needs memory or resources. It's really good at this, so you never have to close an app, with the exception of one stuck due to a bug. In fact, closing an app is counter productive if you open it again later, as now it has to launch from scratch instead of simply resuming. So hiding the option is a feature.