The title of this post is a quote from Ilya Grigorik's post Weak Consistency and CAP Implications. Besides the article being excellent, I thought this idea had something to add to the great NoSQL versus RDBMS debate, where Mike Stonebraker makes the argument that network partitions are rare so designing eventually consistent systems for such rare occurrence is not worth losing ACID semantics over. Even if network partitions are rare, latency between datacenters is not rare, so the game is still on.
The rare-partition argument seems to flow from a centralized-distributed view of systems. Such systems are scale-out in that they grow by adding distributed nodes, but the nodes generally do not cross datacenter boundaries. The assumption is the network is fast enough that distributed operations are roughly homogenous between nodes.