What is more scaring for me, is that Amazon tell you that they have multiple availavility zones on each zone, and recomends you to distribute replicated servers, on each of this zones, for example I have a project with the master database in one zone, and the replica on the other zone.
Why both zones fail?? Are not isolated/independent? Amazon charges you for data transfer between zones. As other says fails the servers, anyone must had backups on other place (S3, or Amazon external).