Mark, you're probably thinking of an article by Al Cudney in the PRA mag many, many years ago. Al was a sort of Bensen groupie, having worked for Bensen off and on. He had a regular column called "Logically Speaking." He said more about that little cable than most of us want to hear.
The main point was that the cable was necessary in towed gyros, because the propulsive thrust was applied at the far front end of the keel. The out-and-down pull of the rope applies a bending load to the mast and keel that was better carried by a straight-line cable right up to the rotor head.
The engine pushes directly against the mast, so there's no bending load on the keel in a powered gyro. The bending load on the mast is still there any time the rotor tilt exceeds the rake angle of the mast, such as in a flare. Hence the cable still gets some use if rigged on a powered gyro.
Al then went on to spin a bunch of tales (some merely humorous) about other benefits of the cable. One of his "serious" side benefits was that the cable would provide crash protection. Obviously, a cable doesn't carry crush loads, only tension loads. Crush, or compression, loads are what you get in crashes. The cable might help restrain a broken-off piece of mast and rotor head in the event of a blade strike -- but that's a bit far-fetched IMHO. Don't bet the farm on it.
