If you're used to your database vendor supplying a full tool chain with the database itself, from server management to application development, PostgreSQL may be a shock to you. Like many successful open source projects, PostgreSQL tries to stay focused on the features it's uniquely good at. This is what the development community refers to as the PostgreSQL core: the main database server, and associated utilities, that can only be developed as a part of the database itself. When new features are proposed, if it's possible for them to be built and distributed out of core, this is the preferred way to do things. This approach keeps the database core as streamlined as possible, as well as allowing those external projects to release their own updates without needing to synchronize them against the main database's release schedule.
Successful PostgreSQL deployments should recognize that a number of additional tools, each with their own specialized purpose, will need to be integrated with the database core server to build a complete system.