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If you look at his post carefully, you'll notice he "collaborated" with another student. He knew he broke the rules, and he was terrified he would get caught. He did not.
Personally, I think students should be able to discuss such assignments with each other, but I don't think you've accurately characterized the situation.
In this case the professor stated that collaboration was absolutely prohibited. Cite: http://news.ycombinator.com/item?id=2776039