The skype app will run indefinitely in the background, killing your battery much sooner than normal. Killing it from the multi-tasking list does prevent this. It is the only app that I am aware of where this makes any difference.
That's because it's a VoiP app - which was listed in the article as being one of the classes of apps allowed to run in the background indefinitely.
Skype is not unique. All VoiP-declared (has to register itself as such and Apple has to approve that classification for publishing on the App Store) apps act like this.
