If your client was paying Oracle already, he should take steps to move away from it, not setup himself up for paying licences forever.
I cringe at having to call Oracle Support. It takes forever and they make you send a ton of files before someone even looks at it.
Unless - as it often happens - someone in high places need to keep justifying a business decision taken 1-2-3 years before.
Bear in mind that minor versions in postgresql are breaking changes. It does not follow semver.
Our last Oracle migration lasted about 2 weeks. When it was over, I decided to upgrade Postgresql too. Including compiling it, it didn't take an hour.
(Also, since Postgresql 10 they changed the numbering scheme so that the major version changes for each 'breaking' release.)
1. This hasn't been true since three releases ago (i.e., PG 10).
2. Before PG10, X.Y _was_ the major version of PostgreSQL, Y was _not_ the minor version. It has never broken backwards compatibility without a major version change.
3. PostgreSQL is much, _much_ older than semver.
Uh, never? I mean, there may be cases where you might need to do that, but I don't want to use a PG built by JoeRandoMacbook somewhere. It's better to use PGDG.
> How often do developers go through the hassle of upgrading databases versions?
As often as they have to. Most places don't upgrade all that often.
AWS is a pretty common "distro" (of sorts). Postgres 12.2 was released 2020-02-13, and AWS RDS supported it on 2020-03-31. You don't have to wait very long to use this.