I've talked to some people about AWS about this, and the reason why they have availability zones is because they don't want to charge you the speed cost of syncing data between zones if your app doesn't need 100% uptime. Generalized replication slows down your app. AWS gives you the option of not having replication or bringing your own.
Outages are hard to avoid, but the pain can be lessened if your customers are aware of the recovery progress and you can deliver on your recovery time goals. Nothing is worse than being down, and leaving customers in the dark to start rumors that your guys are not even aware of the problem.
Edit re your edit on dogfooding: supposedly they use the same tech, just not the same servers, so their AZs are probably separate form ec2s. Also, they're in all of their geographical locations, not just us east.
http://www.slideshare.net/AmazonWebServices/2011-aws-tour-au...