Yes, what you read is correct. "The data stored in Isolated Storage in WP8 device is permanent". And the "Permanent" is as long as your app is in the device. And the data will be deleted, only if the app is uninstalled from the device by the user. Data persists even if the app is closed or even if the phone is rebooted.
Its different with Emulator. Once the emulator is closed, all the data is lost.