Yes, two things conspire to seeing it multiple times; First new people join HN and think "Hmm, this would be interesting to that group" and post it, and second, some people who count karma say "Hmm, that got some good karma back <whenever> I'll post it again." There are some automated controls on the second case and not really any control on the first case.
Both cases provide interesting information, in the first case things that every new person posts are generally pretty widely interesting. In the second case it is interesting to see reputation manipulation through gaming. Some people see a "score" and are compelled to "win."