This is a very timely post for me. My contractor mentioned this to me last week. It caught me totally off guard and seemed counter intuitive to my knowledge of wifi connections. Pretty neat and thank you for sharing.
I think what Wifi-over-Coax is trying to get around is having to coordinate multiple access points. Wifi breaks down particularly horribly when some of the stations and APs can't hear each other. By only having 1 AP, you avoid some of that problem. (Of course, stations can still interfere with each other. So I'm not sure how useful this is in practice.)
I think the idea is that if you already have coax pulled (eg for TVs), you can just connect it to a WiFi access point instead and put an antenna on the other side.