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.
I operated MySQL clusters in the late 2000s. I still am surprised how many hoops you have to jump through to set up replication in PostgreSQL than what you could do - out of the box - with MySQL 15 years ago.
If you're doing tens of millions in revenue and the RDBMS is critical to your operations, I'm a firm believer you need replication. Keep in mind this was the era of spinning rust and a day-old backup could take hours to restore even with a SAN/DAS. A replica was for more than just distributing load, it was for resilience to keep the business healthy and avoid a SPOF.
Risks to the business are more important to me than my enthusiasm for a technology or product.
Replication can be for HA, not just for scale. All depends on your business requirements.
Also replication can be good for other operational reasons, such as zero downtime major version upgrades. Again depends on the business need/expectations.
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.