The Aero Snap feature was something I immediately understood when I started using Windows, and I learned about it just from the feedback you get when you drag a window to the side. You can see that they tested it with real users.
It feels like Apple didn't test their feature with real users at all. It's bad on the desktop, but it's even worse on iPad — I only ever triggered the multi-tasking features accidentally and ended up confused what was going on.