I just went through the old thread and it's comments. It appears google didn't specifically state they were going to end the service. They hinted that links would continue working, but new ones would not be able to be created. It was left a bit open-ended, and that likely made people think the links would work indefinitely.

This seems to be echoed by the archiveteam scrambling to get this archived. I figure they would have backed these up years ago if it was more well known.