Readers may be interested to know that this relates to a wider debate between "Chicago school" economists who believe in the unsustainability of monopoly rents and futility of predatory pricing, and everyone else. I'm probably a "pragmatic Chicagoist" -- allow the monopoly price signal to exist, but not indefinitely. At some point, call in Mr Sherman to break up the party. A priori elimination of the price signal offends my Illinois tendencies, particularly when discriminatory practices are currently the exception rather than the rule. Mark Goldberg has some useful things to say on the terminology to be used for distinguishing service and user discrimination. Again, some see these as part of a continuum which cannot be partitioned, whereas others (including me) see the divide as being acceptably clear.