Jeez, I leave for 5 minutes and you guys get all snippy.
I think what I said here is being overlooked:
Perhaps by throwing the heavy object, the body learns how to perform the throwing motion in a safer manner, and becomes conditioned to do so.
Rather than using weighted balls to do no more than "strengthen", they should be used as a tool to train the body to use different mechanics. Going all the way back to Marshall, weighted balls have been used not just to make the arm stronger - but to reinforce mechanical patterns.
Rather than just looking at football or javelin as being different than baseball and therefore having no relevance - perhaps we should be trying to learn what it is about those motions that allows for a heavier object to be thrown with far less incidence of injury.