...It means you have to check the backup before you set the options for the restore. For my revised code & test above you can infer that my backup did have checksum enabled (or it would have failed). ...
Are you really telling me you still produce backups without using the checksum option ??
I strongly advise to grab any occasion to detect corruption as soon as possible!
As of SQL2005 we've been using checksum for all our backups, no matter Dev/QA/Prod.
It's better to get an alert due to a failed backup, than to have to deal with a corrupted backup file at restore time, when your production database is down or 50devs are out of work.
As of SQLServer 2014 there is a configuration setting which can just set Backup checksum as the default behaviour !
'backup checksum default'
ref: Backup checksum default option in SQL Server 2014[/url]