"Typically users navigate away from an app by pressing the Start button, and then open a new app, just like iPhone owners. Users also don't seem to realize that by repeatedly hitting the back button, they're "stacking" apps. Thus the source claims that Microsoft now believes the Back button just doesn't make sense."
Really? Not that there are a lot of us out there, but this isn't accurate.
First, the back button is how you close applications and repeatedly hitting the back button doesn't stack apps; it's how you close a stack of apps. . .
Second, it is by hitting the start button and opening a new app - THAT is how you stack apps, just like with the iPhone.
Third, the back button doesn't make sense. MS should do two things - 1. make a method to close the app that is its own method - swipe down from the top (like in W8) or something. 2. keep the back button (really handy in a LOT of apps) but make it consistently "go back" instead of "sometimes go back and sometimes exit the program" which I know frustrates me and my wife.
LOVE WP8 aside from that and the lack of apps. I really do - smooth, integrated, easy. . .