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
Where have I seen this before? Oh right.. every time I see "Technology A vs Technology B" comparisons.
Naturally his results are in his favor, otherwise he would not have posted them.