> I think Apple considers the inability to close apps a feature, rather than a bug.

I agree with this statement, but that's because Apple is underestimating its customers. They always aim to achieve things in the simplest ways possible - often meaning that features many customers would like are left out. There is an ongoing debate on whether or not this behavior pays off, but I think that in this case they forgot to fully consider who would be using this feature the most. That is, the tech-savy users with a better idea of what's going on. These users are bothered by the simplicity of the featured, which ends up interfering with their workflows [see below]

> The idea is that you should only be concerned with what app you want to be using at any particular moment, and let the system take care of which ones are still in the background.

The idea is not that you should only be concerned with the app you are using at that moment, but also the app that you are wanting to switch to. That's the simplicity Apple is thinking about: how to get the average user from App A to App B in as little time as possible. However, with the current system, apps never close (unless the device is restarted). What that means is that, after a day or two of use, the multitasking tray/bar is cluttered with every app you have on your phone. For some people (like me), this means HUNDREDS of apps that need to be scrolled through 4 at a time! Now getting from App A to App B doesn't seem so easy. The fact that all these apps that support multitasking have saved their last state and will be quick to start up is good, but the multitasking tray/bar is useless nevertheless. It would be faster for me just to close App A, which I'm currently in, and navigate to App B on the home screen and open it from there where it's last state is still remembered.

On a side note, I'm unsure why Apple gives the user the ability to delete an app from the multitasking tray in the first place. As you said, they only want the user to be concerned with the app they're in and want to let the system take care of the rest. Once you have all your apps in the multitasking tray (which will inevitably happen), the only reason why you would remove a particular app is if you hate it and know you will not use it for a long time. This removes clutter and doesn't have to be done that often, but the feature to delete apps from the multitasking tray still does not make sense to me.

> Could you be more specific about what causes you to need to close 10-20 apps at once, or the workflows that cause you to be troubled by the inability to explicitly terminate apps?

The first part of this question was covered above, but I'd like to answer the second part as well on why we need to terminate apps in a convenient way. Multitasking may be useful if it was only needed between 5 or 10 apps at a time. However, even if those are the ones you use most commonly, there will still be dozens of others that you open at other times - even if it's less frequent. These apps build up and, as I discussed earlier, can only be removed in a tedious way. But, if there was a convenient way of terminating apps when you were done using them, things would be a lot easier. When using your favorite apps you would not completely terminate them, as you would like to keep them running in the background and in your multitasking tray for later use. However with apps that you know you were only using on a rare occasion, you could use a different, but still convenient, hardware function to completely terminate them when you were exiting them - hassle-free. This way you would only have to worry about 5-10 of your favorite apps in the multitasking tray, and not 100-200.

tl;dr - In some cases, Apple simplifies features too much, which results in a lack of functionality. Multitasking is an example of that. The biggest problem with it is that a large number of apps build up in the multitasking tray/bar over time, and therefore there is no easy way to navigate between apps with the multitasking feature. Apple should offer another hardware function that allows users to completely terminate apps (and therefore not put them in the multitasking tray). Users would only keep apps they used often in the tray, and terminate all apps they think they wouldn't use later.