Uh ? iOS has had multitasking enabled for Apple apps since day one (and to third party with jailbreak, it was only a matter to change some flags on programs), it could not have worked as a smartphone without multitasking.
Third party apps have had official access to multitasking since iOS 4.
So, you are very incorrect in your statement. You're confusing an OS feature (multitasking) with a GUI feature (multi-windowing). The later can be enabled without multitasking, you had text based multi-windowing GUI on top of DOS with only task switching and no multitasking whatsoever.