Geek 101: Android and iOS Multitasking Compared | PCWorld
Apparently they are implemented using differernt types of multitasking
FTA
"Android lets the entire app continue to run in the background. A good example is the Nintendo emuators by Youngh. If you use one of these apps then switch to something else, it'll keep running in the background, sound and all, until you decide to close it or your phone runs out of memory.
On the other hand, iOS4 lets apps keep certain features running in the background (but not full apps; for example, you'll be able continue a Skype call or keep listening to your Pandora station while using another app, but the full app isn't running), have its state saved (as with previous versions of the iPhone OS), both, or neither, as desired. In this sense it could be argued that the iPhone OS has always supported multi-tasking via state-saving, and this most recent addition is simply one more tool for developers used to tweak how their app is experienced."