I also live on a boat, in France, and the pressure on mooring places is unbearable in many places, including all of those conveniently close to "good" jobs. This is worsened by the waterways administration's Kafka-like madness. For instance, a boat which has mooring rights in Paris will cost about €600K more than the same one in an unremarkable place (mooring rights are effectively attached to a boat, and non-transferable).
So more extensive evidence shows that when living in a boat becomes popular, prices (in money and inconveniences) do skyrocket.
No, I do think he's right. They might be honestly curious about the details of living on a boat, but in the end not really that interested in pursuing it for themselves. Many think of it as something they might really like to try out for a year or two... tops. others, likely see the appeal but realize that it's not a realistic option for them (spouses, children, pets, etc.). If everyone wanted to live on a boat too, there is no way your costs would stay the same (slip costs would go through the roof).
I think what's keeping people from doing it is fear. Most people don't have the courage to break with deepheld norms such as living in a house or an apartment.