My position is that there a lot of different products out there that cater for different needs and there is no "one size fits all" solution. I can scale Cassandra out to a hundred nodes in minutes on EC2 with no configuration changes. I also have queries in MongoDB that are literally 50x faster than on a SQL database.
I think that for any case where you might be building a new system based on a relational backend, it's basically true (modulo local constraints like "we're an Oracle shop"). The chances that you will need to run a website that needs 100 Cassandra servers any time soon is ... well it's unlikely.
PostgreSQL is a stable, proven workhorse. That's why I like it. My point of view is that you should start with high safety and features and relax those constraints as circumstances demand.
And I comment on lots of different things but have a stronger interests in Apple and Database. So sue me I guess.