No tablet is really that great at multi-tasking and having multiple windows, Windows 8 maybe an exemption but it's still not "officially" out yet for tablets.
Pedro Franceschi has come up with possibly one of the best jailbreak tweaks ever made for the iPad, Quasar.
It's a tweak, available in Cydia, which lets you have multiple apps open at once, all in their own separate windows. And amazingly, from the video it actually looks like it works. (I haven't been able to try it out myself because it hasn't come up in Cydia for me yet). But if you do own an iPad and have it jailbroken this is a must have. It is on the pricey, $10, but it looks well worth it.
It's understandable why iOS and Android don't have this feature by default, because of issues like battery life, processing power, RAM usage and much more. But it's great to see the community coming up with ideas to extend the usage you can get from your devices, whether it be iOS or Android.