Was the success of Rupert Pupkin real in King of Comedy?

There appears to be some debate over this (on IMDb boards and Rotten Tomatoes et al), but I found a wiki snippet that suggests the following:

Film scholar David Bordwell, writing in Film Viewer's Guide, mentioned the (un)reality of the ending as a topic for debate. A number of scenes in the film — Rupert and Jerry in the restaurant, Jerry meeting Rupert after having listened to his tape and calling him a genius, Rupert getting married "live" on Jerry's show — exist solely in Rupert's imagination, and Bordwell suggested that some viewers would think the final sequence is another fantasy.

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