From what I can tell the behaviour in Leopard and Snow Leopard appears to be identical, it's just that Leopard had a falsely-reassuring label for the option whi

From what I can tell the behaviour in Leopard and Snow Leopard appears to be identical, it's just that Leopard had a falsely-reassuring label for the option which has now been changed to a more accurate one. Either OS would have deleted your old backups in the same way. The bottom line is that Time Machine is a backup solution with a certain level of archiving as an added feature; it is not a bulletproof archival solution and shouldn't be relied on for that purpose.