That's an exaggeration.

The idea behind reputation is that it servers as a quick, crude indication of a poster's quality. So far this seems to work, more or less, as people who generally contribute useful content have a high reputation, and those who are rude or break the forum rules (and have been banned before) often have lower reputation. People are obviously free to read a post regardless of the poster's reputation; it's still their call. You can ignore it as well, if you think it's a stupid feature.

The example you gave, for MrBucket, was - in my opinion - an example of the system working as intended. The guy had just registered, already had negative reputation after only 4 or so posts, so there's a possibility that his future posts are also relatively worthless. If you decide to be selective with regards to what posts you read, then that would be a pretty good choice of criteria for what posts to skip.