MySQL folks take a lot of things for granted that are not present in this form in Postgres, and that may be a bad surprise when you try out "the other system".
MySQL for example has a stable and upwards- and slightly-downwards-compatible on-disk format, mostly. Oracle sometimes forgets how important that is and makes changes, or unannounced changes, and then needs to be corrected, hard, by their development partners and testers.
