I love Postgres but its support for sharding, multi-master, and most forms of scaling that aren't just "buy a bigger box" is still way behind most of the NoSQL solutions.
Lots of use cases don't need that kinds of scalability but if you do then Postgres can be more difficult to work with.
Skype used to run entirely on a Postgres cluster before Microsoft bought them. There are lots of examples of large Postgres clusters in the wild. Have you considered hiring an experienced Postgres admin? These types of setups are not impossible.
Lots of use cases don't need that kinds of scalability but if you do then Postgres can be more difficult to work with.