I recall having read about that somewhere. Is that not also required for *any* machinery that'll lift a certain amount of weight? (Like, you'd need it even for a skid steer?)
Presumably, most backhoes wouldn't be heavy enough to require a CDL for on road operation, but something a little bigger, like a Gradall would. Also, presumably, many employers would want their operator to be able to load the machine onto a trailer and haul it to the nesxt site, so that would require a CDL...