This seems like another reason to not rely on Amazon-specific services, other than the obvious vendor lock-in. At least in the event of an instance outage you could conceivably migrate off Amazon to another VPS provider. No one using DynamoDB has an alternative.
Source for service with better uptime than Amazon?
This prevents you from getting too locked in and losing control over your application.
I honestly can't believe that Netflix can't even load their home page without DynamoDB and all this other stuff.
Edit: Looks like Netflix is back online (10:53AM EST)