Upgrades are hard. There was no replication in the before times. The original block-level replication didn't work among different major versions. Slony was a painful workaround based on triggers that amplified writes. Newer PostgreSQL versions are better. Yet still not quite as robust or easy as MySQL. At a certain scale even MySQL upgrades can be painful. At least when you cannot spare more than a few minutes of dow…
"Not as robust as MySQL"? Surely you're joking.
I am a database specialist and have worn the DBA had for many years. I have run MySQL and Postgres in production, both self-hosted and using managed services. Postgres wins on every single dimension that matters, every time. Yes MySQL is easier to setup for non-experts. That counts for nothing.
If you are sticking up for MySQL in this thread... I just don't even know, man.