CL is all they seem to want to do there on the Cox forum.

The idea was bring in more folks as most have Cox engines laying around replaced by something more powerful. Secondly by limiting power the plane design would have to be well thought out to function and perform as intended or as design proportions will allow.
A .061 will compensate a miss calculated or dirty or bad design like slapping a brushless motor on the front would. Of course if its just about type and looks then function need not be rated.