Many people think that force-quitting these apps will at the very least do no harm since “they aren’t running anyways.” The logic of “…you might as well quit, just in case” comes into play...
The very process of quitting an app will use up a measurable amount of battery life. There are times when the device may need those resources and it will quit the app on your behalf, which will drain the battery in the same fashion. However, modern smartphones have an abundance of memory and you would be surprised how often an app can just stay suspended forever. This is doubly true for any app that you are frequently launching and using, these apps in all likelihood will never need to be closed and the repetitive exiting and relaunching can have a very noticeable toll on your battery life.
Federghi obviously didn't go into the same level of detail as Richter, but he clearly has a great grasp of how iOS works and his word should be considered the final one on closing unused apps.
So the next time you have an Apple rumor you want busted, you might try shooting Tim Cook an email.