[jorgeortiz85]

The author is proposing to serve his site entirely from S3, claiming it's better than using a couple of nginx boxes because S3 has eleven nines of durability.

Durability means you will get your data eventually (it will not be lost). Availability means you will get your data right now, which is probably what he really cares about in terms of serving live internet traffic.

Put another way: S3 not infrequently has availability hiccups (files are temporarily unavailable, resulting in a disruption of service), without taking durability hits (your files haven't been lost, you just can't see them right now).