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.
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).
MySQL cluster is highly popular in telecom. http://www.mysql.com/customers/industry/?id=78