Very fast replication
Async and Slow are not the same thing. If you start putting real load on the replication stream, you will start to see delays, but not with a single test command.

From the PostgreSQL Wiki entry you linked to:


  In SR, XLOG records in partially-filled XLOG file are shipped too, implementing record-based log-shipping.'


So streaming replication is exactly that: The stream of updates is transported from master to slave.