Old backup didn't get deleted

At the end of the backup email sent me:

4 servers backed up successfully, 0 had errors. 6 Virtualmin configuration settings backed up successfully. Deleting backups older than 7 days .. .. no backups to delete were found

Backup is complete. Final size was 3.31 GB. Total backup time was 53 minutes, 35 seconds.

However:

$ ls 2009-11-17 2009-11-18 2009-11-22 2009-11-25 $

2009-11-17 should have gotten deleted. Today is the 25th, so the 17th is 8 days old.

Any idea why it didn't get deleted? What am I missing?