those are recently used apps, not running apps, with the most recently used leftmost in the list.

the only apps that run in the background are gps navigation, streaming audio, voip apps and apps that request additional time to complete a task (such as uploading photos to flickr).

everything else is 'frozen' until it's resumed. quitting them will make no difference whatsoever to battery life unless it's one of the above categories. some of them have already been quit by the system if they haven't been run in a while and the memory was needed by another app, even though the icon is still there.