afaik webos has the best multi-tasking system out there and the easiest entry point (since it's just js, css & html)
Android's life-cycle and Bundles makes a developer think about saving app state information from day one. Something as simple as a configuration change, rotating orientation, recreates your Activity.
Since creating and destroying your activity is such a common occurrence you are forced to save the state info.
When the OS needs to kill a background activity to free up space it tends to work.
Really good YouTube video explaining this:
Palm may have nailed the UX, but Android nailed the engineering.
Regardless of merit of their respective UIs, the absolute best thing that could happen to the mobile space is if one completely open mobile OS became completely dominant. And pretty much the only reasonable contender for that role is Android.