Apple states "An application should register [with APN servers] every time it launches and give its provider the current token"

Second, here is the upgrade test sequence and results:

1. Start with iOS4 installed on iPhone4; backup device in iTunes

2. Upgrade to iOS5
   From a previous test, I know that the APN token is now different

3. Restore the backup to the device
   The APN token is now the same as step 1.

4. Reset iOS (clean device)
   The APN Token changes

5. Backup a different phone to iTunes and restore that backup to test device; basically, I'm restoring the "wrong" backup, as if I were switching phones.
   The APN token changes again; further it is distinct and does not match the tokens either the original token or the "cloned" token.

6. Restore the "correct" backup to the device.
   The APN token is now the same as step 1.

7. Lastly, I upgraded the phone to iOS6 (beta2), restored my backup, and re-tested. As expected, the token continued to match the token in step 1.