Don't kid yourself. Reddit has gotten to the point where reposts continue to make the front page because even if a lot of people have seen it, not all have. And I have noticed that the same comments will garner karma.
The problem with websites like Reddit is that they suffer from the so called black swans. A good post can garner karma in the thousands, but a bad one will only have a negative one or two. So, reposting is a great strategy especially when new content is so hard to come by.
