Well, I definitely agree that you have to TRY to fall over board. But when you are drunk or being careless, it could be easy.
With that being said, my first cruise on the Legend in May of 2006 had a jumper. It happened around 1am and from what I heard he was fighting with the wife, security baracaded him on the balcony as a saftey measure and thats when he took his life into his own hands. We spent the next 9hrs circling around looking for him. Never did find him. It was on our way home and instead of getting back at 9AM, it was 9PM.
Its not easy as long as your are smart about it! You are on the boat in the middle of the ocean, chances are... you wont be found.