What I don't like is that they make repeated promises about AZes and features which are repeatedly shown to be untrue. They also have never disclosed their testing methodology, which leads me to assume there isn't much of one. That makes me unlikely to rely on any AWS services I can't myself fully exercise, or which haven't shown themselves to be robust. S3, sure. EC2, sure (except don't depend on modifying instances on any given day during an outage). EBS, oh hell no. ELB, probably not my first choice, and certainly not my sole ft/ha layer. Route 53, which I haven't messed with, actually does seem really good, but since it's complex, I'm scared given the track record of the other complex components.
Thats pretty much SOP in the hosting business, nobody really knows whats going to happen because nobody really knows how to test. Most developers can/do not understand what ops failures are like, and therefore most testing is only superficial.
Edit: Not that I agree or disagree with that SLA. Just noting it is documented somewhere besides a glyph in a legend.