People expecting the ability to close apps could be former Symbian users as well - there is a little cross in the upper right (or left? Not sure) corner in the multitask view of an app to close it immediately. (iOS 7 reminds me more and more of Symbian. Even the icons look very symbian like. But that's another subject.)
BTW, each time when I play with my friends iPhone, I desperately look for the back button LOL
The other day , I tried to use back button on my iPod Touch too.
Lot of android users press search button on WP thinking it was back button (since android back button is on right side)