I've asked the same questions of people that say the way multitasking is implemented is a real hardship but no one's answered. What's the harm? Of "X" hours a day using the phone, what percentage of your time is actually spent active in two (or more) apps simultaneously? And with a powerful processor it shouldn't matter whether a background app is in state or has to be restarted based on the way Android works (see below). I'm not trying to pick a fight I'm trying to understand the depth of the issue.
And since no one's read the article I linked to, here's the cruxt...
Once Android determines that it needs to remove a process, it does this brutally, simply force-killing it. The kernel can then immediately reclaim all resources needed by the process, without relying on that application being well written and responsive to a polite request to exit. Allowing the kernel to immediately reclaim application resources makes it a lot easier to avoid serious out of memory situations.
If a user later returns to an application that's been killed, Android needs a way to re-launch it in the same state as it was last seen, to preserve the "all applications are running all of the time" experience. This is done by keeping track of the parts of the application the user is aware of (the Activities), and re-starting them with information about the last state they were seen in. This last state is generated each time the user leaves that part of the application, not when it is killed, so that the kernel can later freely kill it without depending on the application to respond correctly at that point.
And based on this, the SGS3's handling memory managment just like the One X so there don't appear to be a lot of options for those with special multitasking needs.