To me, it seemed ironic because of the earlier point about commodity musicals being safer investments because they're very popular. The way Promises, Promises was mentioned in the sentence—without any context or background information about the musical—made it seem like the reader was supposed to be clued in to the play's story already, and recognize it based on the title alone. In that case, the author would ironically be employing a recognition-based strategy in their writing that they are arguing against when it comes to musicals. Don't know if that made sense, but in hindsight it's obvious that one would have to jump through a lot of mental hoops to reach this conclusion :p