Of course that gives them a certain level of power of the discourse, but what is the alternative? Community-voted conference structures that fail to take many variables into account that you need to take into account for an enjoyable conference?
If I were invited as a keynote speaker and the conference organizers tell me that the stuff I produced is good, but not suitable for the keynote I wouldn't blame them, but myself. The only instance I could imagine was if they invited me specifically for a spicy topic and my talk was too spicy for them. But a tech talk? Come on.