Netflix puts out some great articles about architecture in the cloud. Auto-scaling, chaos monkey, and how they handle 'steal-time.' Does anyone know of any other company that publishes so much about cloud architecture? This is great stuff!
Most companies their size would use their own servers instead of the cloud.
Using AWS does not magically give you a HA infrastructure when you have a complicated service oriented architecture like Netflix. All the stuff mentioned here are still relevant even if they're running their own DC.