D’oh! It completely flew over my head. Thanks. I’ve heard people who are really into trains bill rail travel as being worth it purely for the experience, so it sounded plausible that they were arguing it seriously

I think it's less a joke than an observation. There's some per hour cost that's approximately fixed, so for a given mode of travel the slower it gets the more expensive it becomes. The lack of investment in rail is a vicious cycle.