Look, there are some places where document DB's solve problems easier/better than SQL, other places kind of suck. For example, plain old object mapping is easie

Look, there are some places where document DB's solve problems easier/better than SQL, other places kind of suck. For example, plain old object mapping is easier with a document DB. Relational DB's tend to make your code look/feel/act more relational and less object oriented. Your object model tends to look just like your table structure. This can be good or bad depending on your viewpoint. There are some approaches to solve some of the author's problems that end up making the Mongo system look and feel a lot more like a SQL system because sometimes data is actually related. The author could have also taken a different approach to his data schema that would have fit more of a non-relational worldview. Software development and architecture is about making choices and working with and around the limitations of your tools. It doesn't matter if PostgreSQL or MongoDB are "better". It's about solving a problem using a set of tools you are comfortable with.