The revelation that Sony charges publishers for bandwidth on PSN explained what had, previously, been a puzzling part of Sony's PlayStation Network (PSN) business model.
In Invisible Engines by David S. Evans, Andrei Hagiu and Richard Schmalensee, the authors point out how various business models are built around software platforms. In particular, a software business model must choose carefully which groups that access the software (developers, end-users, among others) should pay fees for that access. (More on the book here.)
Console platforms charge developers for access to development software and distribution while end-users get the hardware for near cost.
The Xbox Live platform appears to be subsidized to a great extent by the subscription fees paid by the top-tier users. Since Sony doesn't charge users for access to PSN, the publishers are getting charged.