In fairness, you don't have to tune MongDB poorly (deliberately or otherwise) to get poor performance with a workload involving substantial numbers of writes; it's well-documented that there is a global lock (http://www.mongodb.org/display/DOCS/How+does+concurrency+wor...) that prevents reads during write operations.

That said, there are certainly nosql systems with better scaling and concurrency stories* than mongodb out there that he could have benchmarked against. :)

*I'm a cassandra committer