Only the iPad Air 2 has 2GB of RAM. Every other iOS device only has 1GB, which is a severe restriction to true multi-tasking. iPhones only have 1GB of RAM as well, so they couldn't do it even if they wanted to. It's a bit surprising as it limits future functionality. Comparably priced Android phones have 2GB to 4GB of RAM currently and comparably priced Android tablets have had 2GB of RAM for a couple years. Granted, Android OS seems a bit more hungry for tasty RAMs than iOS does.
Android is more ram hungry because it has a different policy on process lifecycle management.
If you hit home on iOS the app you are currently using is expected to pack up and be ready to get evicted from RAM.
If you do the same on Android the app will stay in RAM until there is a capacity crunch. Then the GC will go round waking up the oldest processes and ask them to free up pages. And if that is still not enough, start shutting them down.
Afaik, all iOS devices except the Air2 have 1GB RAM (or less - e.g. iPad2 and iPadMini1 have 512MB). So only Air2 can run two full apps side by side, makes sense.
This seems like a bold claim to throw out without substantiation. It is undeniable that older devices are more resource-limited, and do run the latest OS faster. Sure, Apple probably is trying to push sales of new devices (which is their right—they have no obligation to retrofit the latest-and-greatest features to old devices); but to say that's the only reason seems rather strong.
