I didn’t listen to the accompanying podcast so I might be missing some details.

It strikes me that it seems like 37signals are just using AWS as a glorified virtual machine with maybe some db hosting. To me the big benefit of the cloud is using all the little services they provide, like s3, sns, sqs, CloudSearch ECS, cloudwatch and the list goes on and on. If we were to host all those service ourselves and keep them up to date the operating cost would be huge. Furthermore I work for a site that is very public and has a lot of for instance ddos threats hanging over head. AWS handles lots of ddos threats all the time and they a much better suited for handling that than our own ops team.