I suspect most people never noticed the addition of multitasking in iOS. Suddenly Pandora didn't stop playing when they checked a mail message and their apps reopened much faster, but they probably credited/blamed the app developers for that. I wonder what percentage of users don't even know about the double-click-home menu.

I think multitasking UIs on touch devices (where apps are usually 100% of the screen) are more confusing for users than just going back to the icon on the home screen. Users get that more than one thing is running at a time in a windowed environment -- you can see both of them at the same time if you position your windows properly. I'm not sure they bring that understanding along when they pick up a tablet.