A and C: the engines referred to were installed in training aircraft, doing a lot more touch and goes, landings, ups, downs, and generally more abuse than a privately owned touring aircraft. Noteworthy also that these were rather old aircraft, and occured more or less on certain invividuals than others. And you're absolutely right, it could have been carb icing, but whatever the cause, a gentle "goose" on the throttle works just fine in my experience.