Do you hear music in the background while doing other
things?
Do you see your mail being checked while doing other things?
Do you get background notifications while doing other things?
Do you get appstore apps downloaded while doing other
things?
The iphone is fundamentally built on a mach kernel, which supports multitasking. Taking it out, when they already needed to use it for multitasking for the above tasks, is a silly idea.
