The article is from 1973. I think exact eras are getting a little muddled here. Altair, Mark-8, SCELBI, these are the sort of home computer that came out shortly AFTER this project was published.
You are probably right. I first wrote "many", then edited it to say "some", in the interest of accuracy, since I had only used a few kinds myself, and did not know if all the others supported that feature or not :)