And that is the concept of the "benevolent dictator". If he is a dick, incompetent or does technical stuff you don't like, fork. IMO the best way to run FOSS project, but of course there are others.
It's quite easy for an open source project to just waddle around and start blindly accepting things random developers contribute with no real decision or filtering process (cough PHP). They may verify the code's not buggy or that it at least does something that could be of use to someone, but they generally don't care if it fits in with the overall design and goals of the project.
Having someone who has the complete vision in his head, who's also extremely technical and knows what changes are good and bad, is absolutely invaluable.