Scrum Voids Product Manager
Question: "Scrum defines only three roles: product owner, scrum master, and team. Therefore we do not need a product manager."
Answer: According to the Blackblot PMTK Methodology™, product management is a strategic function in the problem space.
Scrum only pertains to managing a software development project in the solution space.
Accordingly, Scrum cannot bring any claim or pretension to anything outside the development project.