"Whether or not teams and organisations can experience the benefits of Scrum is not determined by the number of intelligent developers that practise it."

True, but Dennis's point was that if SO MANY have been unable to use it with good results, then something is wrong. The Scrum community's response to that is "you are doing it wrong", but if a method is such that very few can use it well, then the method is lacking or not effective most of the time.

Sometimes one encounters a situation where Scrum is working well. But I believe that in those cases it is working because there is someone with good leadership ability who is overseeing the team. In that case, Scrum is not the reason for success: the person who is overseeing the team is the reason for the success. They would have been successful with or without Scrum.