There were a few brief years where an encrypted iTunes backup was a perfect, universally-restorable image of an iOS device. You could back up an iPhone, pop out the SIM card, destroy the original phone, then pop the SIM into a new one, restore the backup, and it would be nearly-impossible to determine that the device was different from a daily UX standpoint. Even MS Exchange email sync would still work.
Then around the time that iCloud K/V store showed up (which may be coincidental), this stopped working. Every app would start up and ask you to log in. Email needs reauthentication. Encrypted iTunes backups aren't terribly useful anymore.
Number one reason why most of my friends and family dont want to buy a new iPhone. They hate the pain and the anxiety of upgrading. And Apple hasn't done anything to make it easier.