The SLA uses great legal weasel words: "AWS will use commercially reasonable efforts to make Amazon EC2 available"
So anything that is beyond commercially reasonable is outside the SLA.
In truth, as with all businesses, the reputation for uptime weighs more heavily than the written contract. It will be interesting to see how the AWS people attempt to make amends.
"Commercially reasonable" is a standard legal term used to define efforts short of "best efforts". It allows for the party also look out for its own commercial interest in a way that's consistent with industry practice. So, for example, if Amazon had to choose between fulfilling the SLA and keeping it's own retail site up, it could be held liable under a "best efforts" standard but not under a "commercially reasonable" standard.
It's kind of unfair to describe these as "weasel words" when it's unlikely that any decent lawyer would let them sign up to something that exposes them to more liability than this. Customers who are using any cloud service provider have to expect reasonable steps to maintain availability, not an absolute promise.
So anything that is beyond commercially reasonable is outside the SLA.
In truth, as with all businesses, the reputation for uptime weighs more heavily than the written contract. It will be interesting to see how the AWS people attempt to make amends.