While apple prides itself on developing software that works so well users never ever need support (sarcasm intended) they have released an official manual to the latest incarnation of the iPhone OS (now simply known as iOS).

The official guide can be found for direct PDF download and is a nice reference to have if needed.

Now if only it were available via iBooks... Hmmmmm.

If the iPhone iOS 4 has one "killer app" it was supposed to be the multitasking feature that was built in.
It took apple such a long time to implement that people reasoned surely it would be a perfect elegant solution...

So why were we given such a "broken" mess with no true multi threaded application support?

When you close or switch almost any app made for any version of iOS prior to 4.0 you are simply closing the app and leaving the icon in the tray.
iOS 4 ready apps can stream music or give directions in the background or can complete a task and send you a notification when done, but never truly stay running (only the apple built apps stay running in their entirety)

But why? Now we are left to micro manage a tray full of icons. Not so elegant apple!

Truthfully the tray full of icons needs to be managed or else you have literally dozens of icons down there and have to hunt around to find what you want.

A better solution is to allow users to specify if they want 3,5, or 10 recents in addition to what's already running. Make the recents a dim sort of appearance so we know they aren't running and mak them stay to the right of whatever is always running.

Apples main concern here FYI is memory. On the iPhone 4 with 512 megabytes or ram it's less of an issue but as someone who has jailbroken and seen the size of mobile safari with a system profiler app I can tell you safari takes up to 150 megs of the 256 in most peoples iPhone 3GS models.

Low ram effects an iPhone just like any other computing device, this is why they do not allow endless apps running.

This is not in defense of apple, these are just logical explanations.