You may think it is easy, but it is not so easy ok. The officer may know better but at the moment of throw, the recruit may panic or forget to do the correct procedure, resulting in an incident.
Years back at Pulau Tekong too, during the live grenade exercise, a recruit panicked and fumbled, and did not follow through the throw. It was short of the target. The OC happened to be at that particular station then and just managed to pull the recruit down but the grenade exploded, resulting in the OC substaining a sharpnel wound in the neck. He was in hospital for more than two weeks and when he returned to Company lines just before POP, we saw for ourselves how much weight he lost and the wound at his neck. It was lucky that this incident was not more serious, if not two lives could have been lost, just in a moment of fumbling.
This is not a laughing matter as depicted in cartoons like Popey the sailor man.:(
Years back, there was also a 2LT who knew how to react---http://www.mindef.gov.sg/imindef/resourcelibrary/cyberpioneer/topics/articles/people/2008/oct08_people.print.noimg.html