One of the problems is that if a story has multiple URLs, this dilutes the traffic. In this case, many people hesitate to link to a PDF, so that scattered the p

One of the problems is that if a story has multiple URLs, this dilutes the traffic. In this case, many people hesitate to link to a PDF, so that scattered the pointers. If multiple people submit the same URL, they get redirected to the original post that they can then vote up, increasing the story's velocity.