I was under the impression that it was device to device, so I can understand apps being installed on an upgraded 32GB N7 that were originally installed on another N7 but not apps from another device?
My first Android device was an SE Xperia X10i, flashing custom ROM's on that and apps were automatically installed when backed up but when I got my S2 none of the apps from my X10i were automatically installed on the S2.
As I said above, when flashing custom ROM's on my S2, apps that were backed up were automatically installed on the S2, as were Wi-Fi passwords. However, none of those apps or Wi-Fi passwords were installed on my N7, not new out of the box, when it was rooted or the three times I have flashed the factory image.
Very inconsistent?