I just read that section and I am unconvinced. To me, it seems the thing that really normalized the single space was HTML. Since it reduces all double spaces to single spaces, single spacing became ubiquitous online. Pervasive, however, doesn't mean better. New doesn't mean improved. Was there a benefit to the old custom of 2 spaces? Well, I think so and I haven't seen an argument for single spacing that makes me think otherwise.