Postgres Pro provides the most actual PostgreSQL version with some additional patches applied and extensions added. Mostly, these are patches already accepted by the PostgreSQL community and committed into PostgreSQL. Also there some patches and extensions developed by Postgres Professional. Users of Postgres Pro thus have early access to some important features and fixes.
Currently the difference between Postgres Pro Enterprise and PostgreSQL is the following:
CREATE INDEX operation in the GiST, GIN, SP-GiST
Postgres Pro Enterprise releases are following the PostgreSQL releases, though sometimes occur more frequently. The Postgres Pro Enterprise versioning scheme is based on the PostgreSQL one and has an additional decimal place.