This isn't really a MySQL-specific problem, but I think it applies here: The article talks about how MySQL AB interprets the license terms, but doesn't really touch on the external validity of their interpretation. What happens when MySQL AB thinks a user needs to purchase a commercial licennse, but the user thinks otherwise?
When I read the GPL, it seems very much at odds with the idea that the hypothetical game company would be in violation of the license (and thus need to pay for a different one.) My point here is not that licenses have ambiguities; that's been said clearly enough. Rather, I'm concerned that MySQL AB might be dependent on its ability to cajole users into doing something they're not legally obligated to do. That's a tenuous position to be in, and I'm concerned that if push ever comes to shove, the results may make dual licensing seem like a less attractive business model.