First, to use Postgres for all those cases you have to learn various aspects of Postgres. Postgres isn't a unified tool which can do everything - instead it's a set of tools under the same umbrella. As a result, you don't save much from similarly learning all those different systems and using Postgres only as a RDBMS. And if something isn't implemented in Postgres better than in a 3rd party system, it could be easier to replace that 3rd party system - just one part of the system - rather than switching from Postgres-only to Postgres-and-then-some. In other words, Postgres has little benefits when many technologies are needed comparing with the collection of separate tools. The article notwithstanding.
Second, Postgres is written for HDDs - hard disk drives, with their patterns of data access and times. Today we usually work with SSDs, and we'd benefit from having SSD-native RDBMSes. They exist, and Postgres may lose to them - both in simplicity and performance - significantly enough.
Still, Postgres is pretty good, yes.