Your entire argument falls apart when you look at all of the companies that chose MySQL over PostgreSQL and are still using them today. Basically every major internet site today relies on MySQL.
First of all, the success of postgresql and mysql are not mutually exclusive. Postgres operates in a lot of markets that MySQL doesn't (as far as I know) like telecom and finance. Postgres gets entirely new users with a variety of use cases, as well as people from Oracle, SQL Server, MySQL, and even some converts from people who tried NoSQL and found it lacking in some way.
An undeniably, there is a shift happening, even in parts of the market that were a MySQL stronghold. Heroku and their customers use postgres for multi-tenancy. Instagram uses postgres for photo-sharing.
I think MySQL has been very complacent because they are the default for a lot of simple web apps, and that keeps their numbers high. They aren't really breaking into new markets -- postgres is winning the geospatial market big time, and is always coming out with new features to break into new markets (personally, I am trying to advance postgres into the temporal database space).
