I would not have risked my business (or budget) on Postgres 8, even with Slony-I. My appreciation for its well-written code and thoughtful architecture simply did not outweigh what it lacked for a reliable operations experience.

MySQL foot guns were mostly under control by 2010, and it was operationally efficient to manage a cluster of MySQL servers in diverse configurations with mostly-known boundaries to what could go wrong.

The Postgres foundations are the same today, but what you can build on top is very different today than it was pre-9.x.