I think that's a simplistic analysis. What you want really depends on the workload characteristics. If you want an immutable data store with high write performance but infrequent reads the Dynamo model works quite well. Writes can be fast with a small quorum (you don't need to persist to disk immediately as you're relying on multiple machines not going down) and read consistency is not usually a huge issue for analytics tasks (who really cares if you miss an event in your processing?) and if it is you can usually afford to wait for quorum reads.
