The growing importance of Content Delivery Network (CDN) in the value chain of content delivery raises concerns about the ``neutrality'' of these players. We propose in this paper a model to analyze the impact of revenue-oriented CDN management policies on the fairness of the competition among two content providers that use CDN services to deliver contents. We show that there exists a unique optimal revenue-maximizing policy for a CDN actor---the dimensioning and allocation of its storage capacity---that depends on prices for service/transport/storage, and on the distribution of content popularity. Using data from the analysis of traces from two major content providers (YouTube Live and justin.tv), we remark that a CDN remains a relatively neutral actor even when one of the content providers it serves tries to monopolize the CDN storage space by implementing an aggressive policy to harm its competitors.