Lack of knowledge of the data all round?
*bias alert* I work for MarkLogic, a NoSQL database vendor.
Many people start with NoSQL because of the schema less nature. Although natural, more important is the type of data and queries you're working with. Where the data fields are known, and relationships are known in advance, RDBMS may be a better fit.
Equally, relational thinking being applied to NoSQL databases is a real problem. This mainly stems to using NoSQL requiring a different way of thinking. Denormalisation vs. Normalisation. Searches over potentially non-existing indexed fields (for document DBs anyway) being more akin to search engine tech vs. query over static, known fields.
I've seen many cases of the opposite of this story. Many people using an excellent RDBMS like Oracle (because it IS excellent) when there is a problem of huge data variety that cannot possibly be known up front, making RDBMS schema design challenging to keep up to date.
It's simply a case of the right tool for the right job.
Other points in this article are more interesting to me. The lack of good documentation and DBA tools is a real problem for NoSQL adoption. One only a few companies *coff* like MarkLogic *coff* have addressed.
Those who point out the religious war on the comments are right too. This type of decision should be about the data, and the problem being looked at. There's enough data problems in the world to warrant both RDBMS and NoSQL databases living side by side. Just like we have mainframes still with RDBMS today.
NoSQL will get there, but not all NoSQL databases are there yet.