You've description of MySQL's dual licensing model describes their current model, which only recently changed. It seems flawed to try to understand MySQL's historical success based on their current policies.
For example, I worked at a small company in 1998 who bought a license a MySQL license, because at that time it was free to run MySQL on Linux, but you had to pay to run in on Windows (and our VC wanted to see the demo on Windows). Of course it also meant we were able to call Monty on the phone and ask him questions. (though the long distance rates could be prohibitive) Neither of these are true about MySQL's current licensing model.