What is different between Piggy's and Simons death in Lord of the Flies?

To quote from the book... 'And in the middle of them, with filthy body, matted hair, and unwiped nose, Ralph wept for the end of innocence, the darkness of man's heart, and the fall through the air of the true, wise friend called Piggy.' When Ralph arrived at the island he was an optimistic boy who believed that his father would soon come and rescue him and that in the meantime he'd have fun on the 'good island' on which he had found himself. Ralph judged the other boys by his own honest, fair and friendly standards and over the course of the story he was forced to revise his judgment. At the end of the book Ralph had found from bitter experience that some people are not fair, honest and good. At the cost of his innocence he had taken part in a 'dance' which had resulted in the violent killing of Simon. Ralph had also witnessed the death of Piggy and had only then realised that the boy, whose real name he'd never even bothered to find out, had actually been his friend. The happy world of feeding ponies and reading books safely in bed had gone for ever and Ralph knew that for the rest of his life he'd have to live with that knowledge.