I've just watched the video, but I have to say, that is only half the reason why not to use a roughing gouge for cross-grain work - the other half is that whereas a bowl gouge is held in its handle by the full diameter of the shaft, a roughing gouge is a forged tool which is held in only by a thin tang. The forces associated with cross-grain turning mean that in the event of a catch, the tang is not substantial enough to prevent the tool from possibly breaking at the point it enters the handle, resulting in, well, an ambulance, and possibly an undertaker. And no, I'm not going to make a video to illustrate my point.