John Gruber of the "Daring Fireball" blog has had a running commentary highlighting this very misconception (see http://daringfireball.net/2012/01/ios_multitasking)
His final word was to point to Fraser Speirs"s excellent post “Misconceptions About iOS Multitasking”.
Part of John Gruber's summary was; "Bottom line: the iOS multitasking bar is not like the command tab switcher on Mac or Windows. It is not a list of currently “running” applications. It is simply a list of your most recently used applications, whether they’re running in the background, suspended in memory, or completely inactive...Emptying this list of applications is simply needless, mindless, busywork. It was absolutely never intended to be used this way and anyone who does this is just wasting their time."