Although Johnny is known to be dramatic, I feel there is truth to what he said. I know of several athletes who, when their performance didn't measure up to a fan's standards, received threats and etc. The article mentions Apollo Ohno. I also remember a (Brazilian?) football player who was killed when he returned to his country after failing in an international.
I also know of many people who receive threats and who never report them. Some feel that they can deal with them on their own, that those making the threats aren't truly serious. There are lots of potential reasons for not reporting. I do wish he had done, though, because it would be easier to stop it if it had been reported from the start.
Someone else mentioned Rudy Galindo, and that he didn't receive threats. One of the major differences between Rudy and Johnny, in addition to those that others have mentioned, is the accessibility of the Internet and public records now. The Internet, and the anonymity it seems to offer, sometimes makes people say things that they'd never say in person or in a real letter. It also makes info like Johnny's parent's phone number much easier to get. The Internet really wasn't as much of a force during Rudy's time.