When I first purchased an Android phone over a year ago the installed OS was Android 2.1 (Eclair). The OS has been updated twice by the carrier since then and now runs Gingerbread. However, I had to restore my phone to factory settings recently and the OS that was reinstalled was Gingerbread. I was expecting it to restore back to 2.1 (Eclair). Is this expected behavior and was the phone reset properly to factory settings? I followed the hard reset instructions here and everything looked correct. However, this was not the factory restore I expected. If this was correct does anyone know how the Gingerbread OS "replaced" the OS that was installed from the factory? I thought the factory settings were "read only." Thank you very much.
This is all from a stock Android phone that has never been rooted.