This paper addresses new questions around media performance as a result of the rise of centralized content portals such as iTunes or MySpace. We first describe the rise of centralized content portals in different media industries, and discuss how these portals are creating a dominant position for themselves by using lock-in strategies. Then we describe the concept of media market performance, and discuss two important media performance concepts: access and diversity. Using scenario analysis, this paper describes three learning scenarios that outline the effects of different configurations of centralized content portals on behavior of publishers, users and advertisers, and through that content on access to and diversity of content.