This is unfortunately not true. Not every DIN valve can be used with yoke with an insert. Many, for example, do not have the required dimple on the back of the valve required to secure the yoke.
Very simple to fix...valves are typically made from brass and shallow depression is easy to make in a pinch by milling it with a drill bit....the likelihood is that a diver is more likely to find themself on a trip with yoke only valves or with convertible DIN valves. Most operators would be disinclined to purchase DIN only valves for their fleet of rental or charter gear. But you are correct, there are DIN only valves out there.
-Z