I think Apple has decided they don't like multitasking on its merits. You can only do one thing at a time, so why run more than one application?
Instead, they're putting their effort into making application launch and exit very fast, and cautioning developers that they should save all important state, and restore it all next time.
Instead, they're putting their effort into making application launch and exit very fast, and cautioning developers that they should save all important state, and restore it all next time.