"DynamoDB uses synchronous replication across multiple data centers for high durability and availability"
This does not seem scalable for OLTP type load on some busy store. Again I think you'll be way better of money wise hosting your own database on real hardware either on prem or colocated
You're forgetting specifics here and the amount of hardware resources thrown into it. I've already told that I am not discussing here FB/Google/Amazon scale stuff. It is their problem and not shared by more regular deployments
This does not seem scalable for OLTP type load on some busy store. Again I think you'll be way better of money wise hosting your own database on real hardware either on prem or colocated